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.

Compare battery energy with fossil fuel and other resources

Lifting off in a large airplane is exhilarating. At a full weight of almost 400 tons, the Boeing 747 requires 90 megawatts of power to get airborne. Take-off is the most demanding part of a flight and when reaching cruising altitude the power consumption decreases to roughly half.

Powerful engines were also used to propel the mighty Queen Mary that was launched in 1934. The 81,000-ton ocean liner measuring 300 meters (1,000ft) in length was powered by four steam turbines producing a total power of 160,000hp (120 megawatts). The ship carried 3,000 people and traveled at a speed of 28.5 knots (52km/h). Queen Mary is now a museum in Long Beach, California.

Table 1 illustrates man’s inventiveness in the quest for power by comparing an ox of prehistoric times with newer energy sources made available during the Industrial Revolution to today’s super engines, with seemingly unlimited power.

SINCE	TYPE OF POWER SOURCE	GENERATED POWER
3000 BC	Ox pulling a load	0.5hp	370W
350 BC	Vertical waterwheel	3hp	2,230W
1800	Watt’s steam engine	40hp	30kW
1837	Marine steam engine	750hp	560kW
1900	Rail steam engine	12,000hp	8,950kW
1936	Queen Mary ocean liner	160,000hp	120,000kW
1949	Cadillac car	160hp	120kW
1969	Boeing 747 jet airplane	100,000hp	74,600kW
1974	Nuclear power plant	1,520,000hp	1,133,000kW

Table 1: Ancient and modern power sources

Large propulsion systems are only feasible with the internal combustion engines (ICE), and fossil fuel serves as a cheap and plentiful energy resource. Low energy-to-weight ratio in terms of net calorific value (NCV) puts the battery against the mighty ICE like David and Goliath. The battery is the weaker vessel and is sensitive to extreme heat and cold; it also has a relatively short life span.

While fossil fuel delivers an NCV of 12,000Wh/kg, Li-ion provides only between 70Wh/kg and 260Wh/kg depending on chemistry; less with most other systems. Even at a low efficiency of about 30 percent, the ICE outperforms the best battery in terms of energy-to-weight ratio. The battery capacity would need to increase 20-fold before it could compete head-to-head with fossil fuel.

Another limitation of battery propulsion over fossil fuel is fuel by weight. While the weight diminishes when being consumed, the battery carries the same deadweight whether fully charged or empty. This puts limitations on EV driving distance and would make the electric airplane impractical. Furthermore, the ICE delivers full power at freezing temperatures, runs in hot climates, and continues to perform well with advancing age. This is not the case with a battery as each subsequent discharge delivers slightly less energy than the previous cycle.

Power from Primary Batteries

Energy from a non-rechargeable battery is one of the most expensive forms of electrical supply in terms of cost per kilowatt-hours (kWh). Primary batteries are used for low-power applications such as wristwatches, remote controls, electric keys and children’s toys. Military in combat, light beacons and remote repeater stations also use primaries because charging is not practical. Table 2 estimates the capability and cost per kWh of primary batteries.

	AAA CELL	AA CELL	C CELL	D CELL	9 VOLT
Capacity (alkaline)	1,150mAh	2,850mAh	7,800mAh	17,000mAh	570mAh
Energy (single cell)	1.725Wh	4.275Wh	11.7Wh	25.5Wh	5.13Wh
Cost per cell (US$)	$1.00	$0.75	$2.00	$2.00	$3.00
Cost per kWh (US$)	$580	$175	$170	$78	$585

Table 2: Capacity and cost comparison of primary alkaline cells. One-time use makes energy stored in primary batteries expensive; cost decreases with larger battery size.

Power from Secondary Batteries

Electric energy from rechargeable batteries is more economical than with primaries, however, the cost per kWh is not complete without examining the total cost of ownership. This includes cost per cycle, longevity, eventual replacement and disposal. Table 3 compares Lead acid, NiCd, NiMH and Li-ion.

	LEAD ACID	NICD	NIMH	LI ION
Specific energy (Wh/kg)	30–50	45–80	60–120	100–250
Cycle life	Moderate	High	High	High
Temperature performance	Low when cold	-50°C to 70°C	Reduced when cold	Low when cold
Applications	UPS with infrequent discharges	Rugged, high/low temperature	HEV, UPS with frequent discharges	EV, UPS with frequent discharges
Cost per kWh ($US) Load leveling, powertrain	$100-200	$300-600	$300-600	$300–1,000

Table 3: Energy and cost comparison of rechargeable batteries. Although Li-ion is more expensive than Lead acid, the cycle cost may be less. NiCd operates at extreme temperatures, has the best cycle life and accepts ultra-fast charge with little stress.

 

Power from Other Sources

To reduce the fossil fuel consumption and to lower emissions, governments and the private sector are studying alternate energy sources. Table 4 compares the cost to generate 1kW of power that includes initial investment, fuel consumption, maintenance and eventual replacement.

Fuel type	Equipment to generate 1kW	Life span	Cost of fuel per kWh	Total cost per kWh
Li-ion Powertrain	$500/kW (20kW battery costing $10,000)	2,500h (repl. cost $0.40/kW)	$0.20	$0.60 ($0.40 + $0.20)
ICE in vehicle	$30/kW ($3,000/100kW)	4,000h (repl. cost $0.01/kW)	$0.33	$0.34 ($0.33 + $0.01)
Fuel cell – portable – mobile – stationary	$3,000–7,500	2,000h 4,000h 40,000h	$0.35 -> -> ->	$1.85 – 4.10 $1.10 – 2.25 $0.45 – 0.55
Solar cell	$12,000, 5kW system	25 years	$0	~$0.10*
Electricity electric grid	All inclusive	All inclusive	$0.20 (average)	$0.20

Table 4: Cost of generating 1kW of energy. Estimations include the initial investment, fuel consumption, maintenance and replacement of the equipment. Grid electricity is lowest.

^{* Amortization of investment yielding 200 days of 5h/day sun; declining output with age not included.}

Power from the electrical utility grid is most cost-effective. Consumers pay between $0.06 and $0.40US per kWh, delivered with no added maintenance cost or the need to replace aging power-generating machinery; the supply is continuous. (The typical daily energy consumption per household in the West is 25kW.)

The supply of cheap electricity changes when energy must be stored in a battery, as is the case with a solar system that is backed up by a battery and in the electric powertrain. High battery cost and a relatively short life can double the electrical cost if supplied by a battery. Gasoline (and equivalent) is the most economical solution for mobility.

The fuel cell is most effective in converting fuel to electricity, but high equipment costs make this power source expensive in terms of cost per kWh. In virtually all applications, power from the fuel cell is considerably more expensive than from conventional methods.

Our bodies also consume energy, and an active man requires 3,500 calories per day to stay fit. This relates to roughly 4,000 watts in a 24-hour day (1 food Calorie* = 1.16 watt-hour). Walking propels a person about 40km (25 miles) per day, and a bicycle increases the distance by a factor of four to 160km (100 miles). Eating two potatoes and a sausage for lunch propels a bicyclist for the afternoon, covering 60km (37 miles, a past-time activity I often do. Not all energy goes to the muscles alone; the brain consumes about 20 percent of our intake. The human body is amazingly efficient in converting food to energy; one would think that the potato and sausage lunch could hardly keep a laptop going for that long. Table 5 provides the stored energies of calories, proteins and fat in watt-hours and joules.

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.

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*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.

Discover what causes short runtimes

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.

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.