When it comes to the words’ lithium battery’ it’s safe to say that lately, these two words have generated a lot of confusion, fear, and speculation. So, it’s no wonder you might ask yourself, “why on Earth would anyone use Lithium batteries?” But rest assured, we’ve done our homework. At Himax, we’ve dedicated over a decade of our time on, research & development, learning, design, and optimization of our products, to ensure that we always provide customers with safe technology and innovative solutions. Before we can get into what makes our Lithium batteries safe, let’s cover the basics.
Lithium 101
Lithium was discovered in 1817 by Swedish Chemist, Johan August Arfwedson. You might remember seeing “Li,” on the periodic table on your school teacher’s wall, but Arfwedson first called it ‘lithos’, which means stone in Greek. Li is a soft, silvery-white alkali metal and its high-energy density makes it a great choice to give batteries an extra boost.
1. Safety:
LiFePO4 is more chemically stable, and it is incombustible, which means that it is not prone to thermal runaway (and remains cool at room temperature). It can also withstand high temperatures without decomposing, and it is not flammable. The bottom line is, you don’t have to worry about it exploding or catching alight on the job.
2. Sustainable:
LiFePO4 batteries have a longer cycle life, and the fact that they are rechargeable makes them sustainable. In essence, you can keep using a LiFePO4 batter over and over again. LiFePO4 is a nontoxic material and doesn’t give off dangerous or hazardous fumes, which makes it safe for you and the environment too.
3. Long lasting:
A Lithium LiFePO4 battery does not need to be fully charged to use. This means that you can connect several batteries in parallel, without damaging the batteries which are less charged than others. It can also be discharged quickly without damaging the cells either. LiFePO4 batteries have a shallow rate of self-discharge, which means they can be left standing for months and not run out of juice or cause permanent damage. They also have a longer and better life cycle, ranging in the thousands. (2000 cycles).
4. Efficiency:
A Lithium LiFePO4 battery has a much higher charging rate, it charges quicker than other batteries, and charging it is effortless. It also requires zero maintenance, which means you’ll experience minimal downtime and maximum productivity when you use Lithium LiFePO4 battery tug. Lithium LiFePO4 batteries are lighter and occupy less space, which makes pushing and pulling a compact tug with a Lithium LiFePO4 battery, ergonomic. Our Lithium LiFePO4 battery is versatile and easily intergrade with many of our tugs. Since the battery is rechargeable and simple to charge, which means they are ready to move when you are.
5. Performance:
Lithium LiFePO4 batteries have an optimal energy density in both volume and weight and have good specific energy, which means the battery can give the necessary power when needed. It’s also worth mentioning that Lithium LiFePO4 batteries have excellent cycling performance too.
Bonus: Battery management system
Our Lithium battery comes standard with a battery management system (BMS) to manage the rechargeable Lithium LiFePO4 battery. How it does this is by monitoring the battery’s state and the cells. It also collects various sets of data to calculate and control the battery’s environment. One of the critical functions of the BMS is to balance the cells to ensure that the battery can perform at its best while protecting it by observing its voltage and temperature to avoid cell failure.
Wondering how to charge a deep cycle battery the right way? You’ve come to the right place!
So you took the plunge and invested in a deep cycle battery. You’re excited about spending endless hours on the water and powering your trusted trolling motor and favorite fishing gadgets. But in order for your battery to continue working for years to come, you’ve got to put in a smidge of work to keep things running smoothly.
Now of course, if you have a lithiumdeep cycle battery, your maintenance “to do” list is pretty short. Nearly as short as Santa’s naughty kids gift list. That’s because lithium batteries don’t need electrolyte “topping-up”, cleaning, or any of that nonsense that lead-acid batteries require.
However, there is one thing you must do for any battery–even lithium. You must charge it the right way!
Why Do You Need To Charge Your Battery Correctly?
Why does it matter how you charge your deep cycle battery? Well, charging the right way can actually affect your battery’s performance and lifespan. For lead acid batteries, overcharging can ruin them. Leaving them at a partial state of charge can do a real number on them too.
Luckily, those no-nos don’t exist for lithium marine batteries. You can use them past 50% battery capacity without damaging them. And you don’t have to charge them right away after using up your charge. This is super convenient when coming home from a fun but exhausting day out on the lake.
But there are a few things you’ll want to keep in mind when charging a deep cycle battery, even if it’s ionic lithium. Read on to find out how to charge a deep cycle battery the right way!
Cycles of Battery Charging
A deep cycle battery is designed to attain a considerable depth of discharge, and then be recharged to full capacity for many cycles during its lifespan. A typical deep cycle battery cycle would begin with the battery at 100 percent capacity, then drain the battery to between 20 and 50 percent of its original capacity, then recharge to 100 percent.
The normal depth of discharge of your batteries will also affect their lifespan. A battery that is often pushed to 50% depth of discharge will live longer than one that is frequently pushed to a higher depth of discharge. Repeated shallow discharge (5-10%) of a deep cycle battery, on the other hand, correlates to reduced lifespans.
Again, quality deep cycle batteries are designed to be drained and then recharged to full capacity from a practical viewpoint. On the water, you really don’t need to be conservative with your batteries. Drain them, and when you get back to dry ground, recharge them with a charger to automatically restore their full capacity.
How to Charge a Deep Cycle Battery Correctly
Ready to juice up your battery? Here’s how to charge a deep cycle safely and efficiently:
Choose the correct charger type.
It’s a no-brainer that the BEST charger for a deep cycle battery is the one that’s built specifically for its type. That means an ionic lithium battery will charge better with a lithium battery charger.
Sure, it’s possible to “mix-and-match” battery types and chargers. But you run the risk of your charger reaching different voltage limits than your battery can handle. It’s possible to damage your battery, or at the very least, you’ll see an error code and your battery won’t charge.
Also, consider the fact that a correctly-matched charger will help your battery charge faster. For example, ionic lithium batteries can take a higher current. They charge much faster than other types, but only when paired with the correct charger.
So how do you choose the right charger? Simply put, read the charger’s description. It will specify what type(s) of batteries you can use it to charge. For lithium deep cycle batteries, we suggest Ionic single chargers and Ionic bank chargers. Built for lithium LiFePO4 marine batteries, they are smart chargers that supply constant voltage and stop charging once they reach max voltage. Some models may also be used to charge lead acid and AGM batteries.
Onboard chargers for batteries – the options.
Both offer the same set of key advantages:
Charges your batteries more quickly and conveniently.
Up to four 12V lithium batteries can be charged at the same time.
Can be used to charge both lead-acid and AGM batteries.
The cable is five feet long.
Charge status is shown via colored LEDs.
When utilizing Ionic Lithium Batteries, the Ionic Lithium app displays the charge level.
Lightweight
Affordable
These onboard chargers are perfect for competitive fishermen and boaters. They’re also ideal for anyone looking for the most advanced onboard battery chargers available on the market, and people who hate to wait long for their battteries to charge.
Portable chargers for batteries – the options.
Sometimes, installing an onboard charger is impossible or impracticable. Take for example, a tiny boat with limited storage, or a trolling motor-powered kayak or canoe — in these cases, you’ll probably need a portable battery charger. It’s probably impractical otherwise, and that’s okay — you’ve got options.
12v Portable Chargers
24v Portable Chargers
Both of these chargers are single bank, and offer the same basic functions. These “Smart” chargers for 12V LiFePO or lead-acid batteries are constant current, constant voltage (CCCV). When 14.6V is achieved, these smart chargers cease charging.
Both are great options for fishermen and boaters who need portable battery charging for their trips.
Choose the right charger voltage/amps.
Once you know what type of charger you need, you need to pick one with the right amount of voltage and amps. For example, a 12V charger is compatible with a 12V battery. Within the 12V battery category, you can choose from different charge currents (i.e. 4A, 10A, 20A).
To choose the right amount of amps, check the amp hour (Ah) rating of your battery. Make sure the amp rating isn’t higher than the amp hour rating of your battery. Using a charger with an amp rating that is too high can damage your battery.
You can also use a bank charger to charge multiple batteries at once.
Charge in the right conditions.
Did you know that high and low temperatures can affect your marine battery? Lithium batteries are the most resilient of the bunch. You can charge them at temperatures between -4°F – 131°F (0°C – 55°C) with no risk of damage. But the optimum charging temperature for Ionic Lithium Batteries is above freezing. If you need to charge your battery below freezing temps, no need to fret. Our 12V 300Ah battery is a beast of a battery and comes equipped with a heater, so no more worries about freezing temperatures!
How to Charge a Deep Cycle Battery Correctly (& Safely): Step by Step
Once you have the right charger, charging your battery is a cinch. Here’s what to do, step by step:
Make sure the battery terminals are clean.
First, connect the red (positive) cable to the red terminal. Then connect the black (negative) cable to the black terminal.
Plug in the charger. Turn it on.
If using a smart charger, you can “set it and forget it”. It will stop charging on its own. Ionic lithium chargers feature Bluetooth capabilities that let you check charge status on your phone. Other chargers, like those used for lead acid batteries, may require you to set a timer and disconnect it once it’s charged.
To disconnect, unplug the charger. Remove the black cable, then the red one.
Now you know how to charge a deep cycle battery safely and correctly. Here’s to many more adventure out on the water!
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Are you wanting to use solar power off grid? If so, you’re going to need off grid solar batteries–and they’d better be reliable.
If you use a grid-tied or hybrid system, it’s possible to run your solar without batteries. But as soon as you go off the grid, batteries become an essential part of your setup. Without them, you can’t store solar energy for use at a later time. You know, times when the sun’s not shining.
And what if you invest in solar batteries, only for them to malfunction, or run out of energy earlier than expected? Well, if the skies are dark, unfortunately your house or RV will be too.
So save yourself the trouble. Keep reading to discover the pros and cons of each battery type so you can choose the best one!
Off Grid Solar Batteries Aren’t Just for Camping
Years ago, solar batteries had their habitat in remote campsites and mountaintop cabins. Today, they’re still essential for boondocking and dry camping but with “grid defection” on trend, solar setups are making their way towards many towns and cities.
People are going off grid in places where grid power is available. They’re building eco-friendly tiny houses that completely rely on solar power. Others are installing solar panels on rooftops as backup power in places where the grid’s frequently unreliable. Some are saving big money by using solar only, and relying on the grid as a backup.
So now, more than ever, off grid solar batteries need to be reliable, long-lasting, and efficient. But not all batteries are created equal. Below, we’ll discuss the different types of off grid solar batteries so you can decide which is best for you.
What Are the Best Solar Batteries?
There’s no denying that lead acid batteries have been used in off grid solar setups for a long time. They’re the “OG” (original) batteries, and in the early days of solar energy, you wouldn’t see a setup without them.
But technology has evolved since then. So while lead acid batteries still get the job done, we wouldn’t say they’re the best off grid solar batteries on the market. They may be the most affordable up–front, but their benefits don’t go far beyond that.
Now each battery type has its pros and cons. Let’s compare the top contenders for off grid solar batteries, specifically lead acid, AGM, sealed gel, and lithium. These are the four most popular solar batteries available today and that’s why each is worth discussing. So let’s get to it!
Lead Acid Batteries
Lead acid batteries have been around for over 150 years. Most folks who use them as off grid solar batteries do so because of their low up-front cost.
Pros
Low cost
Good for short-term backup solar power
Cons
Short lifespan (3-5 years). Can be shorter if overcharged or not maintained correctly.
Require maintenance (watering, cleaning).
Contain toxins that may harm the environment.
Aren’t leak-proof and must be stored in a ventilated area.
Not ideal for remote off-grid sites that aren’t visited frequently, because of maintenance needs.
Usable capacity is 50%.
Sealed Gel Cell Batteries
Sealed gel cell batteries have electrolytes stored in gel form. This prevents them from spilling. They are similar to AGM batteries.
Pros
Can tolerate long periods without being charged.
Low self-discharge rate.
Longer cycle life than AGM batteries.
Maintenance free.
Cons
Medium-high cost.
Not suitable for constant use in remote places (where replacement is difficult).
Charges slowly.
Short lifespan (2-5 years).
Limited ability to deliver peak power.
50% usable capacity.
AGM Off Grid Solar Batteries
AGM stands for absorbed glass mat. These are similar to gel cell batteries and are sealed.
Pros
Low maintenance
Good for intermittent use, such as in a vacation cabin
Performs better than gel batteries when delivering peak power
Spill-proof, will not leak
Low self-discharge rate
Cons
Medium to high cost
Not suitable for constant use in remote places (where replacement is difficult).
Susceptible to overcharging.
Short lifespan( 4-6 years). May be shorter if overcharged.
50% usable capacity.
Lithium Off Grid Solar Batteries
LiFePO4 lithium batteries are the newest off grid solar battery type. They’re currently the most reliable battery on the market for solar setups. Here’s why:
Pros
Longest lifetime of any battery type.
Protected from overcharging or undercharging.
Eco-friendly, toxin-free, and will not leak.
Maintenance-free.
Lowest lifetime cost of any battery type.
Fastest charging battery type.
Great for both long-term, short-term, and intermittent use
Does not need to be replaced often; good for remote locations.
Most energy-efficient of all battery types.
Usable capacity is 80-100%, the most of any battery type.
Best battery for hot and cold climates.
Cons
Higher up-front cost
Which Solar Batteries Should You Choose?
Everyone’s energy needs are different. Lead acid or gel type batteries may work if you’re looking to test a solar setup short-term to see if it’s a right fit for you.
But when you consider efficiency, reliability and lifetime cost, it’s clear that lithium comes out on top as the best contender among all off grid solar batteries. So don’t let the slightly steeper up-front cost rain on your parade! Keep things sunny (and your electricity running smoothly) by powering your setup with lithium.
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Know how to apply an equalize charge and not damage the battery.
Stationary batteries are almost exclusively lead acid and some maintenance is required, one of which is equalizing charge. Applying a periodic equalizing charge brings all cells to similar levels by increasing the voltage to 2.50V/cell, or 10 percent higher than the recommended charge voltage.
An equalizing charge is nothing more than a deliberate overcharge to remove sulfate crystals that build up on the plates over time. Left unchecked, sulfation can reduce the overall capacity of the battery and render the battery unserviceable in extreme cases. An equalizing charge also reverses acid stratification, a condition where acid concentration is greater at the bottom of the battery than at the top.
Experts recommend equalizing services once a month to once or twice a year. A better method is to apply a fully saturated charge and then compare the specific gravity readings (SG) on the individual cells of a flooded lead acid battery with a hydrometer. Only apply equalization if the SG difference between the cells is 0.030.
During equalizing charge, check the changes in the SG reading every hour and disconnect the charge when the gravity no longer rises. This is the time when no further improvement is possible and a continued charge would have a negative effect on the battery.
The battery must be kept cool and under close observation for unusual heat rise and excessive venting. Some venting is normal and the hydrogen emitted is highly flammable. The battery room must have good ventilation as the hydrogen gas becomes explosive at a concentration of 4 percent.
Equalizing VRLA and other sealed batteries involves guesswork. Observing the differences in cell voltage does not give a conclusive solution and good judgment plays a pivotal role when estimating the frequency and duration of the service. Some manufacturers recommend monthly equalizations for 2–16 hours. Most VRLAs vent at 34kPa (5psi), and repeated venting leads to the depletion of the electrolyte, which can lead to a dry-out condition.
Not all chargers feature equalizing charge. If not available, the service should be performed with a dedicated device.
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Learn about unique applications and what features to look for when choosing a battery.
Consumers are the first to hear about an apparent battery breakthrough. To get top media attention, the new super battery promises to also satisfy the need for electric vehicle (EV). Personal mobility is an emotional issue that cannot be suppressed, even if it harms the environment. The industrial space, on the other hand, is more conservative and it appears to lag behind. Not so. Industry is rational and understands the many constraints of the battery by focusing on reliability, economy, longevity and safety.
Batteries for Traction
Wheelchairs, scooters and golf cars mostly use lead acid batteries. Even though heavy, lead acid works reasonably well and only moderate attempts are made to switch to other systems Li-ion will be a natural alternative in many applications.
Although Li-ion is more expensive than lead acid, the cycle cost can be lower because of the longer life. A further advantage of Li-ion over lead- and nickel-based batteries is the low maintenance. Li-ion can be left at any state-of-charge without adverse side effects. In contrast, NiCd and NiMH need an occasional full discharge to prevent memory and lead acid requires a saturated charge to prevent sulfation.
Most wheelchairs and golf cars are still powered with lead acid, so are forklifts. With forklifts, the heavy weight is less of an issue, but the long charging time is a disadvantage for warehouses operating 24 hours a day. Some forklifts are fitted with fuel cells that charge the battery while the vehicle is in use. The battery can be made smaller but not eliminated because the fuel cell has poor power delivery and has a sluggish ramp-up on demand; the battery remains the primary power source.
The heavier the wheeled application is, the less suitable the battery becomes. This does not prevent engineers from looking into large battery systems to replace the polluting internal combustion engine (ICE). One such application is the Automatic Guided Vehicle (AGV) system at ship ports. AGVs run 24 hours a day and the vehicles cannot be tied up for lengthy charging intervals. Li-ion solves this in part by replacing the very large 10-ton, 300kWh lead acid with a battery that is lighter and can be charged more quickly. But very large batteries have a limitation because of weight, charging time and infrastructure and the fuel cell may solve large traction systems as described in BU-1005 if burning fossil fuel is not an option.
However, no economical battery solution exists yet for large traction systems and burning fossil fuel cannot be fully avoided. While a modern Li-ion battery delivers about 150Wh/kg of energy, the net calorific value (NCV) of fossil fuel is over 12,000Wh/kg. Even at the low 25-percent efficiency of an ICE engine, the energy from a battery is fractional compared to fossil fuel (see BU-1007: Net Calorific Value). Furthermore, the ICE can operate in extreme cold and heat, a task the battery struggles to meet.
Batteries for Aviation
The duty of batteries on board an aircraft is to feed navigation and emergency systems when the Auxiliary Power Unit (APU) is off or during an emergency in flight. The battery provides power for braking, ground operation and starting the APU. In the event of engine failure, the batteries must supply energy from 30 minutes to 3 hours. Each aircraft must also have enough battery power to facilitate a safe landing. During flight, the electrical power is supplied by generators and, similar to a car, the on-board battery could be disconnected if so required.
Most commercial jetliners use flooded nickel-cadmium. Starting a large aircraft begins by spooling the APU, a small turbine engine located at the tail section of an airplane. This takes significantly longer and requires more energy than cranking a reciprocating engine of similar size. The spooling speed of the APU must be sufficiently high to attain compression for self-sustained ignition. Starting takes about 15 seconds and consumes 15kW of energy. Once running, an air compressor or hydraulic pump jumpstarts the large jet engines one-by-one.
Smaller aircraft often have sealed lead-acid. Although heavier than NiCd, lead acid requires less maintenance. The 12 and 24V aviation batteries are rated in IPP (current peak power)* and IPR (current power rating)** rather than CCA (cold cranking amps) as is common in the automotive industry. IPP and IPR are the International Electrotechnical Commission (IEC 60952-1) standard for aircraft batteries and FAA TSO-C173 that allow a battery to spool each engine for 25–40 seconds at high current.
Modern jet fighters spool the jet engines with Li-ion, so does the Boeing 787 Dreamliner. The Airbus 350 offers the option of either chemistry. As the on-board functions of an airliner move from hydraulic to electrical, larger batteries are required. The higher energy-dense Li-ion satisfies this demand better than NiCd and lead acid. However, unexpected Li-ion failure with serious consequences may move airplane makers back to NiCd. All batteries are subject to breakdowns; there are also reported heat failures with NiCd, but these can be better managed than Li-ion.
NiCd provides durability and reliable service, but it needs high maintenance that includes exercising the battery to eliminate memory. The service of the main-ship battery consists of a total discharge and shorting each cell for 24 hours with a strap. The battery is also checked for capacity with a battery analyzer. Smaller NiCd batteries have different service requirements.
Although aircraft carry many different batteries aboard, their sole purpose is to start the engine and provide backup power when the engines are off. Large aircraft will continue to fly on fossil fuel as batteries are not yet practical for propulsion. Small battery-powered airplanes are being tried for pilot training and to fly short hops but these are experimental only. Weight and reliability on an aging battery remain major concerns.
*Ipp:
Peak current delivered at 0.3 seconds into a 15 second controlled discharge at a constant terminal voltage of half the nominal battery voltage.
**Ipr:
This is the discharge current at the conclusion of a 15 second controlled discharge at a constant terminal voltage of half the nominal battery voltage.
Batteries for Aerospace
Early satellites used NiCd batteries, and this led to the discovery of the “memory” phenomenon. The battery followed a routine discharge schedule but when more energy was demanded, the battery could remember. The voltage would drop as if to protest against unwanted overtime.
NiCd was replaced by nickel-hydrogen as a battery with an exceptional long service life. Entrepreneurs tried to introduce this amazing battery for commercial use but high price and large size spoiled market acceptance. Each cell costs around $1,000 and has the appearance of a small steam engine with a steel pressure tank.
Li-ion is the battery of choice for satellites. It is light-weight, easy to charge, durable and cycles well. Li-ion can dwell in any SoC for an extended length of time without adverse side effects; it has low self-discharge and is virtually maintenance free.
The Mars Curiosity Rover uses specially designed lithium nickel oxide cells (LiNiCo) in 8S2P formation (eight cells in series and two in parallel) that is only partially charged and discharged to stretch longevity. Under this regime, the life span is four years and roughly 700 sol. (The term sol is used by planetary astronomers to refer to the duration of a solar day on Mars.) The 43Ah cells, of which two are in parallel, have a maximum discharge C-rate of 0.55C.
NASA wants Li-ion batteries to last for 7 years and 37,000 cycles with a DoD of 40 to 60 percent. NASA labs reveal that end-of-life is connected with the growth of the SEI layer on the anode, loss of cathode material, loss of conductive path, plating of metallic lithium and electrolyte oxidation. Large 140Ah Li-ion cells are in development that promise to last up to 18 years. (See also BU-808B: What causes Li-ion to die?)
Stationary Batteries
With a growing choice of batteries for energy storage systems (ESS), the selection should not be based on price alone. Cost per kWh says little without also examining the total cost of ownership that includes cost per cycle, longevity and eventual replacement.
Lead acid is well suited for duties that need only occasional discharges. The flow battery and sodium-sulfur battery work well for large systems requiring regimented discharges, while lithium ion is recommended for small to medium systems delivering short discharging with fast charging ability multiple times a day.
Traditionally, stationary batteries have been lead acid. Size and weight is of lesser concern, and the limited cycle count does not pose a problem when the batteries are seldom discharged. Large stationary batteries are mostly flooded and require regular checking of the electrolyte level. This maintenance can be reduced with an automatic watering system.
Valve-regulated lead acid (VRLA) is the low-maintenance version of the flooded lead acid. It is said that VRLA can be installed and forgotten, but this is often taken to the extreme in that the batteries get neglected. Maintenance includes checking the voltage, internal resistance and sometimes capacity levels.
Applications that are exposed to hot and cold temperatures as well as those requiring deep cycling are often served by flooded nickel-cadmium. These batteries are more rugged than lead acid but are roughly four times the cost. Flooded nickel-cadmium batteries are non-sintered and are less subject to memory that the sintered versions, which are sealed, but some maintenance is still required. NiCd is the only battery that can be rapidly charged with minimal stress.
Many stationary batteries are also served by Li-ion. Li-ion comes with many advantages, but the battery does not perform as well as NiCd and lead acid at low temperature. Another battery that is making a comeback for stationary use is nickel-iron.Inventor Thomas Edison promoted NiFe for the electric vehicle, but it eventually lost out to lead acid due to high cost and high self-discharge. Improvements have eliminated some of the failings, and the superior durability of this battery is gaining renewed interest.
Energy Storage Systems (Grid Storage Batteries)
Renewable energy sources such as wind and sun do not provide a steady stream of energy, nor do they always harmonize with user demand. Large energy storage systems (ESS) called load leveling or grid storage batteries are needed to provide a seamless service.
ESS enjoys a large growth trajectory to move from coal and oil to renewable resources. ESS installations in South Africa alone are estimated to reach 1,500MWh by 2021. Chemistries under consideration are flow batteries, Li-ion, lead acid and zinc-bromine. Zinc-bromine is a type of hybrid flow battery that can be regarded as an electroplating machine. During charge, zinc electroplates onto conductive electrodes forming bromine; the process reverses on discharge. Another leading ESS battery is the high temperature sodium-sulfur battery.
Storing energy to supply peak shaving power is not new. Hydroelectric power stations use excess electricity to pump water back up to the reservoir at night for use the next day. With an efficiency factor of 70–85 percent, pumped hydro is easier to manage than adjusting the generators to the exact power need. Pumping compressed air into large underground cavities and underwater balloons are also being used to store energy.
Flywheels also serve as energy storage. Large electric motors rev up one-ton flywheels when excess energy is available to supply brief energy deficiencies. High-speed flywheels spin at over 30,000 rpm on magnetic bearings in a vacuum chamber. Electric motors/generators with permanent magnets charge and discharge the kinetic energy on demand.
Modern flywheels replace steel with carbon fibers to withstand higher rotations of up to 60,000 rpm. Energy increases by the square of speed, providing four times the power at a reduced weight. Should the flywheel fail, the housing prevents shrapnel form escaping.
Using flywheels to store kinetic energy is not new. In the 1940s and 1950s, city busses in Switzerland were powered by flywheels. An electric motor would spin a 3-ton flywheel to 3,000 rpm in 3 minutes. Turning into a generator, the motor would then transform the energy back into electricity. Each charge would yield for 6km (3.75mi) on a flat road. The bus was pollution-free but the gyroscope action resisted changing direction on a windy road.
Load leveling is gravitating towards Li-ion because of small footprint, low maintenance and long life. Li-ion does not suffer from sulfation as lead acid does when not fully charged periodically. This can be a major drawback with installations when demand exceeds supply. Li-ion also has the benefit of being light-weight and semi-portable for installations in remote locations. The negatives of Li-ion are its high price and low performance at cold temperature. A further drawback is the inability to charge below freezing.
Li-ion has come down in price and Table 1 provides a cost comparison with lead acid for grid storage applications. Although the initial price of Li-ion is higher than lead acid, the cost per cycle is lower in deep-cycle applications. Li-ion is said to gain in market share but lead acid will keep its stronghold.
LEAD ACID
LI-ION
Battery cost
$20,000
$52,000
Lifespan
500 cycles at 50% DoD
1,900 cycles at 90% DoD
Cost per cycle
$40
$28
Table 1: Cost comparison of lead acid and Li-ion for renewable energy. Li-ion has a higher initial cost but is lower on the cost per cycle. Prices are estimated. Courtesy: http://www.powertechsystems.eu/en/technics/lithium-ion-vs-lead-acid-cost-analysis
The energy output of a large industrial wind turbine is 1 megawatt (MW) and more; the biggest units have grown to 10MW. Several turbines form a wind farm that produces 30–300MW. To fathom a megawatt, 1MW feeds 50 houses or a Walmart superstore.
Not all renewable energy systems include load leveling batteries. The batteries simply get too large and the investment cannot always be justified. If supported by batteries, a 30MW wind farm uses a storage battery of about 15MW. This is the equivalent of 20,000 starter batteries or 176 Tesla S 85 EVs with an 85kWh battery each. The cost to store energy in a battery is high, and some say it doubles the cost to a direct supply.
The battery management system (BMS) keeps the battery at about 50 percent charge to allow absorbing energy on wind gusts and delivering on high load demands. Modern BMS can switch from charge to discharge in less than a second. This helps stabilize the voltage on transmission lines, also known as frequency regulation.
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Not all battery energy can or should be used on discharge; some reserve is almost always left behind on purpose after the equipment cuts off. There are several reasons for this.
Most mobile phones, laptops and other portable devices turn off when the lithium-ion battery reaches 3.00V/cell on discharge. At this point the battery has about 5 percent capacity left. Manufacturers choose this voltage threshold to preserve some energy for housekeeping, as well as to reduce battery stress and allow for some self-discharge if the battery is not immediately recharged. This grace period in empty state can last several months until self-discharge lowers the voltage of Li-ion to about 2.50V/cell, at which point the protection circuit opens and most packs become unserviceable with a regular charger.
Power tools and medical devices drawing high current tend to push the battery voltage to an early cut-off prematurely. This is especially apparent at cold temperatures and in cells with high internal resistance. These batteries may still have ample capacity left after the cutoff; discharging them with a battery analyzer at a moderate load will often give a residual capacity of 30 percent. Figure 1 illustrates the cut-off voltage graphically.
Figure 1: Illustration of equipment with high cut-off voltage.
Portable devices do not utilize all available battery power and leave some energy behind.
To prevent triggering premature cutoff at a high load or cold temperature, some device manufacturers may lower the end-of-discharge voltage. Li-ion in a power tool may discharge the battery to 2.70V/cell instead of 3.00V/cell; Li-phosphate may go to 2.45V/cell instead of 2.70V/cell, lead acid to 1.40V/cell instead of the customary 1.75V/cell, and NiCd/NiMH to 0.90V/cell instead of 1.00V/cell.
Industrial applications aim to attain maximum service life rather than optimize runtime, as it is done with consumer products. This also applies to the electric powertrain; batteries in a hybrid cars and electric vehicle electric vehicles are seldom fully discharged or charged; most operate between 30 and 80 percent state-of-charge when new. This is the most effective working bandwidth; it also delivers the longest service life. A deep discharge to empty followed a full charge would cause undue stress for the Li-ion. Similarly, satellitesuse only the mid-band of a battery called the “sweet zone.” Figure 2 illustrates the “sweet zone” of a battery.
Figure 2: Sweet zone of a Lithium-ion battery to extend life.
Operating Li-ion in the “sweet zone” prolongs battery life because a partial cycle is less stressful than a full cycle. As the capacity fades with use, the battery management system (BMS) may engage the full working range of the battery.
Elevated internal resistance makes alkaline and other primary batteries unsuitable for high load applications. The resistance rises further as the cell depletes. This causes an early cutoff with the device drawing some current, and much energy is left behind. Primary batteries have high capacities and perform well when new, but they soon lose power like a deflating balloon.
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Become familiar with battery fade and how the ready light can deceive the user.
Folks have been using rechargeable batteries for over 100 years but this marvelous power source is still poorly understood. The battery is a silent worker that delivers energy until it quits of exhaustion and old age. It is more prone to failure than most other parts in a system. Much is expected but little is given in return. With a shorter life span than the host device, battery replacement becomes an issue, and the “when” and “what if” are not well defined by the device manufacturer. Some batteries are replaced too soon but most stay too long.
A portable system works well when the batteries are new but confidence drops after the first packs need replacing due to capacity fade. In time, the battery fleet becomes a jumble of good and bad batteries, and that’s when the headache begins. Battery management mandates that all batteries in a fleet are kept at an acceptable capacity level. Packs that fall below a given threshold must be replaced to keep system integrity. Battery failure occurs most often on a heavy traffic day or in an emergency when more than normal service is demanded.
Batteries exhibit human-like qualities and need good nutrition. Care begins by operating at room temperate and discharging them at a moderate current. There is some truth as to why batteries cared for by an individual user outperform those in a fleet; studies can back this up.
Charging is generally well understood, but the “ready” light is misconstrued. Ready does not mean “able.” There is no link to battery performance, nor does the green light promise full runtime. All batteries charge fully, even if weak; “ready” simply means that the battery is full.
The capacity a battery can hold diminishes with age and the charge time shortens with nickel-based batteries and in part also with lead acid, but not necessarily with Li-ion. Lower charge transfer capability that inhibits the flow of free electrons prolongs the charge time with aged Li-ion. (See BU-409a: Why do Old Li-ion Batteries Take Long to Charge?)
A short charging time propels faded batteries to the top, disguised as combat ready. System collapse is imminent when workers scramble for freshly charged batteries in an emergency; those that are lit-up may be deadwood. (Note that the charge time of a partially charged battery is also shorter.) Figure 1 shows the “ready” light that is known to lie.
Figure 1: The “ready” light lies. The READY light indicates that the battery is fully charged. This does not mean “able” as there is no link between “ready” and battery performance.
The amount of energy a battery can hold is measured in capacity. Capacity is the leading health indicator that determines runtime and predicts end of battery life when low. A new battery is rated at 100 percent, but few packs in service deliver the full amount: a workable capacity bandwidth is 80–100 percent. As a simple guideline, a battery on a two-way radio having a capacity of 100 percent would typically provide a runtime of 10 hours, 80 percent is 8 hours and 70 percent, 7 hours.
The service life of a battery is specified in number of cycles. Lithium- and nickel-based batteries deliver between 300 and 500 full discharge/charge cycles before the capacity drops below 80 percent.
Cycling is not the only cause of capacity loss; keeping a battery at elevated temperatures also induces stress. A fully charged Li-ion kept at 40°C (104°F) loses about 35 percent of its capacity in a year without being used. ( See BU:808: How to Prolong Lithium-based Batteries ). Ultra-fast chargers and harsh discharging is also harmful. This cuts battery life to half, and hobbyists can attest to this.
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Discover what a battery needs to get going and maintain a long life.
In many ways, a battery behaves like a human being. It senses the kindness given and delivers on the care given. It is as if the battery has feelings and returns on the benevolence bestowed. But there are exceptions, as any parent raising a family will know; and the generosity conferred may not always deliver the anticipated returns.
To become a good custodian, you must understand the basic needs of a battery, a subject that is not taught in school. This section teaches what to do when the battery is new, how to feed it the right “food” and what to do when putting the pack aside for a while. Chapter 7 also looks into restrictions when traveling with batteries by air and how to dispose of them when their useful life has passed.
Just as a person’s life expectancy cannot be predicted at birth, neither can we date stamp a battery. Some packs live to a great old age while others die young. Incorrect charging, harsh discharge loads and exposure to heat are the battery’s worst enemies. Although there are ways to protect a battery, the ideal situation is not always attainable. This chapter discusses how to get the most from our batteries.
Priming a New Battery
Not all rechargeable batteries deliver the rated capacity when new, and they require formatting. While this applies to most battery systems, manufacturers of lithium-ion batteries disagree. They say that Li-ion is ready at birth and does not need priming. Although this may be true, users have reported some capacity gains by cycling after a long storage.
“What’s the difference between formatting and priming?” people ask. Both address capacities that are not optimized and can be improved with cycling. Formatting completes the fabrication process that occurs naturally during use when the battery is being cycled. A typical example is lead- and nickel-based batteries that improve with usage until fully formatted. Priming, on the other hand, is a conditioning cycle that is applied as a service to improve battery performance during usage or after prolonged storage. Priming relates mainly to nickel-based batteries.
Lead Acid
Formatting a lead acid battery occurs by applying a charge, followed by a discharge and recharge. This is done at the factory and is completed in the field as part of regular use. Experts advise not to strain a new battery by giving it heavy duty discharges at first but gradually working it in with moderate discharges, like an athlete trains for weight lifting or long-distance running. This, however, may not be possible with a starter battery in a vehicle and other uses. Lead acid typically reaches the full capacity potential after 50 to 100 cycles. Figure 1 illustrates the lifespan of lead acid.
Figure 1: Lifespan of Lead Acid
A new lead acid battery may not by fully formatted and only attains full performance after 50 or more cycles. Formatting occurs during use; deliberate cycling is not recommended as this would wear down the battery unnecessarily.
Deep-cycle batteries are at about 85 percent when new and will increase to 100 percent, or close to full capacity, when fully formatted. There are some outliers that are as low as 65 percent when tested with a battery analyzer. The question is asked, “Will these low-performers recover and stand up to their stronger brothers when formatted?” A seasoned battery expert said that “these batteries will improve somewhat but they are the first to fail.”
The function of a starter battery lies in delivering high load currents to crank the engine, and this attribute is present from the beginning without the need to format and prime. To the surprise of many motorists, the capacity of a starter battery can fade to 30 percent and still crank the engine; however, a further drop may get the driver stranded one morning. See also BU-904: How to Measure Capacity)
Nickel-based
Manufacturers advise to trickle charge a nickel-based battery for 16–24 hours when new and after a long storage. This allows the cells to adjust to each other and to bring them to an equal charge level. A slow charge also helps to redistribute the electrolyte to eliminate dry spots on the separator that might have developed by gravitation.
Nickel-based batteries are not always fully formatted when leaving the factory. Applying several charge/discharge cycles through normal use or with a battery analyzer completes the formatting process. The number of cycles required to attain full capacity differs between cell manufacturers. Quality cells perform to specification after 5–7 cycles, while lower-cost alternatives may need 50 or more cycles to reach acceptable capacity levels.
Lack of formatting causes a problem when the user expects a new battery to work at full capacity out of the box. Organizations using batteries for mission-critical applications should verify the performance through a discharge/charge cycle as part of quality control. The “prime” program of automated battery analyzers (Cadex) applies as many cycles as needed to attain full capacity.
Cycling also restores lost capacity when a nickel-based battery has been stored for a few months. Storage time, state-of-charge and temperature under which the battery is stored govern the ease of recovery. The longer the storage and the warmer the temperature, the more cycles will be required to regain full capacity. Battery analyzers help in the priming functions and assure that the desired capacity has been achieved.
Lithium-ion
Some battery users insist that a passivation layer develops on the cathode of a lithium-ion cell after storage. Also known as interfacial protective film (IPF), this layer is said to restrict ion flow, cause an increase in internal resistance and in the worst case, lead to lithium plating. Charging, and more effectively cycling, is known to dissolve the layer and some battery users claim to have gained extra runtime after the second or third cycle on a smartphone, albeit by a small amount.
Scientists do not fully understand the nature of this layer, and the few published resources on this subject only speculate that performance restoration with cycling is connected to the removal of the passivation layer. Some scientists outright deny the existence of the IPF, saying that the idea is highly speculative and inconsistent with existing studies. Whatever the outcome on the passivation of Li-ion may be, there is no parallel to the “memory” effect with NiCd batteries that require periodic cycling to prevent capacity loss. The symptoms may appear similar but the mechanics are different. Nor can the effect be compared to sulfation of lead acid batteries.
A well-known layer that builds up on the anode is the solid electrolyte solid electrolyte interface (SEI). SEI is an electrical insulation but has sufficient ionic conductivity to allow the battery to function normally. While the SEI layer lowers the capacity, it also protects the battery. Without SEI, Li-ion might not get the longevity that it has. (See BU-307: How does Electrolyte Work?)
The SEI layer develops as part of a formation process and manufacturers take great care to do this right, as a batched job can cause permanent capacity loss and a rise in internal resistance. The process includes several cycles, float charges at elevated temperatures and rest periods that can take many weeks to complete. This formation period also provides quality control and assists in cell matching, as well as observing self-discharge by measuring the cell voltage after a rest. High self-discharge hints to impurity as part of a potential manufacturing defect.
Electrolyte oxidation (EO) also occurs on the cathode. This causes a permanent capacity loss and increases the internal resistance. No remedy exists to remove the layer once formed but electrolyte additives lessen the impact. Keeping Li-ion at a voltage above 4.10V/cell while at an elevated temperature promotes electrolyte oxidation. Field observation shows that the combination of heat and high voltage can stress Li-ion more than harsh cycling.
Lithium-ion is a very clean system that does not need additional priming once it leaves the factory, nor does it require the level of maintenance that nickel-based batteries do. Additional formatting makes little difference because the maximum capacity is available right from the beginning, (the exception may be a small capacity gain after a long storage). A full discharge does not improve the capacity once the battery has faded — a low capacity signals the end of life. A discharge/charge may calibrate a “smart” battery but this does little to improve the chemical battery. (See BU-601: Inner Working of a Smart Battery.) Instructions recommending charging a new Li-ion for 8 hours are written off as “old school,” a left-over from the old nickel battery days.
Non-rechargeable Lithium
Primary lithium batteries, such as lithium-thionyl chloride (LTC), benefit from passivation in storage. Passivation is a thin layer that forms as part of a reaction between the electrolyte, the lithium anode and the carbon-based cathode. (Note that the anode of a primary lithium battery is lithium and the cathode is graphite, the reverse of Li-ion.)
Without this layer, most lithium batteries could not function because the lithium would cause a rapid self-discharge and degrade the battery quickly. Battery scientists even say that the battery would explode without the formation of lithium chloride layers and that the passivation layer is responsible for the battery’s existence and the ability to store for 10 years.
Temperature and state-of-charge promote the buildup of the passivation layer. A fully charged LTC is harder to depassivate after long storage than one that was kept at a low charge. While LTC should be stored at cool temperatures, depassivation works better when warm as the increased thermal conductivity and mobility of the ions helps in the process.
CAUTION
Do not apply physical tension or excessive heat to the battery. Explosions due to careless handling have caused serious injuries to workers.
The passivation layer causes a voltage delay when first applying a load to the battery, and Figure 2 illustrates the drop and recovery with batteries affected by different passivation levels. Battery A demonstrates a minimal voltage drop while Battery C needs time to recover.
Figure 2: Voltage behavior when applying a load to a passivated battery.
Battery A has mild passivation, B takes longer to restore, and C is affected the most. Courtesy EE Times
LTC in devices drawing very low current, such as a sensor for a road toll or metering, may develop a passivation layer that can lead to malfunction, and heat promotes such growth. This can often be solved by adding a large capacitor in parallel with the battery. The battery that has developed a high internal resistance is still capable of charging the capacitor to deliver the occasional high pulses; the standby time in between is devoted to recharging the capacitor.
To assist in sulfation prevention during storage, some lithium batteries are shipped with a 36kΩ resistor to serve as a parasitic load. The steady low discharge current prevents the layer from growing too thick, but this will reduce the storage life. After 2-year storage with the 36kΩ resistor, the batteries are said to still have 90 percent capacity. Another remedy is attaching a device that applies periodic discharge pulses during storage.
Not all primary lithium batteries recover when installed in a device and when a load is applied. The current may be too low to reverse the passivation. It is also possible that the equipment rejects a passivated battery as being low state-of-charge or defective. Many of these batteries can be prepared with a battery analyzer (Cadex) by applying a controlled load. The analyzer then verifies proper function before engaging the battery in the field.
The required discharge current for depassivation is a C-rate of 1C to 3C (1 to 3 times of the rated capacity). The cell voltage must recover to 3.2V when applying the load; the service time is typically 20 seconds. The process can be repeated but it should take no longer than 5 minutes. With a load of 1C, the voltage of a correctly functioning cell should stay above 3.0V. A drop to below 2.7V means end-of-life. (See BU-106: Primary Batteries)
These lithium-metal batteries have high lithium content and must follow more stringent shipping requirements than Li-ion of the same Ah. (See BU-704a: Shipping Lithium-based Batteries by air) Because of the high specific energy, special care must be taken in handling these cells.
CAUTION
When charging an SLA with over-voltage, current limiting must be applied to protect the battery. Always set the current limit to the lowest practical setting and observe the battery voltage and temperature during charge.
In case of rupture, leaking electrolyte or any other cause of exposure to the electrolyte, flush with water immediately. If eye exposure occurs, flush with water for 15 minutes and consult a physician immediately.
Wear approved gloves when touching the electrolyte, lead and cadmium. On exposure to the skin, flush with water immediately.
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Know how to maintain a battery fleet and eliminate the risk of unexpected downtime.
A battery performs well when new but the capacity soon begins to fade with use and time. To assure reliable service during the life span of the battery, design engineers oversize the pack to include some spare capacity. This is similar to carrying extra fuel in an airplane to enable a waiting pattern or attempt a second landing approach when so required.
New batteries operate (should operate) at a capacity of 100 percent; replacement occurs when the packs fade to about 80 percent. All batteries must include a secure level of spare capacity to cover worst-case scenarios.
In addition to normal capacity fade, cold temperature lowers the capacity, especially Li-ion. The capacity loss of a Li-ion Energy Cell is about 17 percent at 0°C (32°F), 34 percent at –10°C (14°F) and 47 percent at –20°C (–4°F). Power Cells perform better at cold temperature with lower cold-related capacity losses than Energy Cells.
Lack of spare capacity is a common cause of system failures. This commonly happens during heavier than normal traffic or in an emergency. During routine operations, marginal batteries can hide comfortably among their peers, but they will fail when put to the test. A battery maintenance program as part of quality control assures that all batteries in the fleet are within the required performance range.
Figure 1 illustrates the breakdown of a battery that includes capacity fade and spare capacity. Adding 20 percent for fade and 20 percent for spare as a safety net leaves only 60 percent for the actual capacity. Such a generous allowance may not be practical in all cases.
Figure 1: Calculating spare battery capacity.
Spare capacity should be calculated for a worst-case scenario. The allowable capacity range is 80-100%; a spare capacity of 20 percent is recommended for critical use. Allow more capacity reserve when operating at cold temperature.
To verify sufficient spare capacity in a battery fleet, identify batteries that are close to retirement and spot-check their capacities after a busy day with a battery analyzer. The Cadex analyzer provides this function on the “Prime” program in that it applies a discharge before charge. The first reading on the display reflects the spare capacity and the second represents the full capacity after a charge.
If packs with fringe capacity levels come back from a full-day shift with less than 10 percent of spare capacity, raise the pass/fail target capacity from 80 to 85 percent to gain five extra points. If, on the other hand, these old-timers come back with 30 percent before charging, keep them longer by lowering the target capacity to, say, 70 percent. Knowing the energy needs for each application during a typical shift increases battery transparency. This improves reliability and creates a sweet spot between risk management and economics.
While most batteries are replaced when the capacity fades to 80 percent, scanners in some warehouses can be kept longer because they may not require all available capacity during an 8-hour shift. If this is the case, the target capacity can safely be set to 70 percent while maintaining ample spare capacity. A starter battery in a vehicle still cranks the motor with a capacity of 40 percent. The discharge is short and the battery recharges right away. Allowing the capacity to drop much further might prevent the battery from turning the engine on a cold morning, stranding the driver.
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Discover familiar battery formats, some of which going back to the late 1800s.
Early batteries of the 1700s and 1800s developed in Europe were mostly encased in glass jars. As batteries grew in size, jars shifted to sealed wooden containers and composite materials. In the 1890s, battery manufacturing spread from Europe to the United States and in 1896 the National Carbon Company successfully produced a standard cell for widespread consumer use. It was the zinc-carbon Columbia Dry Cell Battery producing 1.5 volts and measuring 6 inches in length.
With the move to portability, sealed cylindrical cells emerged that led to standards sizes. The International Electrochemical Commission (IEC), a non-governmental standards organization founded in 1906, developed standards for most rechargeable batteries. In around 1917, the National Institute of Standards and Technology formalized the alphabet nomenclature that is still used today. Table 1 summarizes these historic and current battery sizes.
Size
Dimensions
History
F cell
33 x 91 mm
Introduced in 1896 for lanterns; later used for radios; only available in nickel-cadmium today.
E cell
N/A
Introduced ca. 1905 to power box lanterns and hobby applications. Discontinued ca. 1980.
D cell
34.2 x 61.5mm
Introduced in 1898 for flashlights and radios; still current.
C cell
25.5 x 50mm
Introduced ca. 1900 to attain smaller form factor.
Sub-C
22.2 x 42.9mm
16.1mL
Cordless tool battery. Other sizes are ½, 4/5 and 5/4 sub-C lengths. Mostly NiCd.
B cell
20.1 x 56.8mm
Introduced in 1900 for portable lighting, including bicycle lights in Europe; discontinued in in North America in 2001.
A cell
17 x 50mm
Available in NiCd, NiMH and primary lithium; also in 2/3 and 4/5 sizes. Popular in older laptops and hobby applications.
AA cell
14.5 x 50mm
Introduced in 1907 as penlight battery for pocket lights and spy tool in WWI; added to ANSI standard in 1947.
AAA cell
10.5 x 44.5mm
Developed in 1954 to reduce size for Kodak and Polaroid cameras. Added to ANSI standard in 1959.
AAAA cell
8.3 x 42.5mm
Offshoot of 9V, since 1990s; used for laser pointers, LED penlights, computer styli, headphone amplifiers.
4.5V battery
67 x 62
x 22mm
Three cells form a flat pack; short terminal strip is positive, long strip is negative; common in Europe, Russia.
9V battery
48.5 x 26.5
x 17.5mm
Introduced in 1956 for transistor radios; contains six prismatic or AAAA cells. Added to ANSI standard in 1959.
18650
18 x 65mm
16.5mL
Developed in the mid-1990s for lithium-ion; commonly used in laptops, e-bikes, including Tesla EV cars.
26650
26 x 65mm
34.5mL
Larger Li-ion. Some measure 26x70mm sold as 26700. Common chemistry is LiFeO4 for UPS, hobby, automotive.
14500
14x 50mm
Li-ion, similar size to AA. (Observe voltage incompatibility: NiCd/NiMH = 1.2V, alkaline = 1.5V, Li-ion = 3.6V)
21700*
21 x 70mm
New (2016), used for the Tesla Model 3 and other applications, made by Panasonic, Samsung, Molicel, etc.
32650
32 x 65mm
Primarily in LiFePO4 (Lithium Iron Phosphate)
Table 1: Common old and new battery norms. * The 21700 cell is also known as 2170. IEC norm calls for the second zero at the end to denote cylindrical format.
Standardization included primary cells, mostly in zinc-carbon; alkaline emerged only in the early 1960s. With the growing popularity of the sealed nickel-cadmium in the 1950s and 1960s, new sizes appeared, many of which were derived from the “A” and “C” sizes. Beginning in the 1990s, makers of Li-ion departed from conventional sizes and invented their own standards.
A successful standard is the 18650 cylindrical cell. Developed in the early 1990s for lithium-ion, these cells are used in laptops, electric bicycles and even electric vehicles (Tesla). The first two digits of 18650 designate the diameter in millimeters; the next three digits are the length in tenths of millimeters. The 18650 cell is 18mm in diameter and 65.0mm in length.
Other sizes are identified with a similar numbering scheme. For example, a prismatic cell carries the number 564656P. It is 5.6mm thick, 46mm wide and 56mm long. P stands for prismatic. Because of the large variety of chemistries and their diversity within, battery cells do not show the chemistry.
Few popular new standards have immerged since the 18650 appeared in ca. 1991. Several battery manufacturers started experimenting using slightly larger diameters with sizes of 20x70mm, 21x70mm and 22x70mm. Panasonic and Tesla decided on the 21×70, so has Samsung, and other manufacturers followed. The “2170” is only slightly larger than the 18650 it but has 35% more energy (by volume). This new cell is used in the Tesla Model 3 while Samsung is looking at new applications in laptops, power tools, e-bikes and more. It is said that the best diameters in terms of manufacturability is between 18mm and 26mm and the 2170 sits in between. (The 2170 is also known as the 21700.) The 26650 introduced earlier never became a best-seller.
The 32650 is primarily available in LiFePO4 (Lithium Iron Phosphate) with a nominal voltage of 3.2V/cell and a typical capacity of 5,000mAh. The dimensions are 32x65mm; true sizes may be slightly larger to allow for insulation and labels.
On the prismatic and pouch cell front, new cells are being developed for the electric vehicle (EV) and energy storage systems (ESS). Some of these formats may one day also become readily available similar to the 18650, made in high energy and high power versions, sourced by several manufacturers and sold at a competitive prices. Prismatic and pouch cells currently carry a higher price tag per Wh than the 18650.
The EV and ESS markets advance with two distinct philosophies: The use of a large number of small cells produced by an automated process as low cost, as done by Tesla, versus larger cells in the prismatic and pouch formats at a higher price per Wh for now, as done by other EV manufacturers. We have not seen clear winners of either format; time will tell.
Looking at the batteries in mobile phones and laptops, one sees a departure from established standards. This is due in part to the manufacturers’ inability to agree on a standard, meaning that most consumer devices come with custom-made cells or battery packs. Compact design and market demand are swaying manufacturers to go their own way. High volume with planned obsolescence allows the production of unique sizes in consumer products.
In the early days, a battery was perceived “big” by nature, and this is reflected in the sizing convention. While the “F” nomenclature may have been seen as mid-sized in the late 1800s, our forefathers did not anticipate that a battery resembling a credit card could power computers, phones and cameras. Running out of letters towards the smaller sizes led to the awkward numbering of AA, AAA and AAAA.
Since the introduction of the 9V battery in 1956, no new formats have emerged. Meanwhile portable devices lowered the operating voltages to between 3V and 5V. Switching six cells (6S) in series to attain 9V is expensive to manufacture, and a 3.6V alternative would serve better. This imaginary new pack would have a coding system to prevent charging primaries and select the correct charge algorithm for secondary chemistries.
Starter batteries for vehicles also follow battery norms that are based on the North American BCI, the European DIN and the Japanese JIS standards. These batteries are similar in footprint to allow swapping. Deep-cycle and stationary batteries follow no standardized norms and the replacement packs must be sourced from the original maker. The attempt to standardize electric vehicle batteries may not work and might follow the failed attempt to standardize laptop batteries in the 1990s.
Future Cell Formats
Standardization for Li-ion cell formats is diverse, especially for the electric vehicle. Research teams, including Fraunhofer,* examine and evaluate various formats and the most promising cell types until 2025 will be the pouch and the 21700 cylindrical formats. Looking further, experts predict the large-size prismatic Li-ion cell to domineer in the EV battery market. Meanwhile, Samsung and others bet on the prismatic cell, LG gravitates towards the pouch format and Panasonic is most comfortable with the 18650 and 21700 cylindrical cells.
Large battery systems for ESS, UPS, marine vessels and traction use mostly large format pouch cells stacked with light pressure to prolong longevity and prevent delamination. Thermal management is often done by plates drawing the heat between layers to the outside and liquid cooling.
Safety Concerns with Rechargeable Cells
Off-the-shelf cells have primarily been non-rechargeable and for public use. Typical applications are spares for flashlights, portable entertainment devices and remote controls. Accidental shorting with keys or coins in a jean pocket only causes an alkaline cell to heat up and not catch fire. The voltage collapses on an electrical short because of high internal resistance; removing the short stops the reaction. (See BU-304c: Battery Safety in Public.)
Rechargeable cells are normally encapsulated in a for-purpose pack. The exception is the 18650 available as a spare cell for vaping. Looking like a large AA cell, these Li-ion cells can inflict acute injury, even death, if mishandled. If shorted, an unprotected Li-ion cell will vent with flame. Once the jet-like explosion is in progress, removing the short no longer stops the reaction and the cell burns out. Li-ion’s ability to deliver high power is a characteristic that must be respected. (See also BU-304c: Battery Safety in Public.)
The 18650 cell can be made safe with built-in safety circuits described in BU-304b: Making Lithium-ion Safe. With protection, excessive current shuts the cell down, either momentarily by a heat element or permanently by an electric fuse. But the fused 18650 has the disadvantage of shutting down when high current is needed on purpose, such as vaping. Spare cells for vaping are normally unprotected.
Another cause of fire is low quality no-brand cells. Li-ion batteries are safe if made by a reputable manufacturer. Many aftermarket cells do not have the same rigorous safety checks as brand name products have. (See BU-810: What Everyone Should Know About Aftermarket Batteries.) Cells can also be damaged by stress related to heat, shock, vibration and incorrect charging or loading.
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