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How to Charge a Deep Cycle Battery Properly

Fisherman driving a gray and blue bass boat on the lake.

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 lithium deep 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

Two fishermen driving in a red bass boat on the lake.

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!

Two fishermen driving in a bass boat on the lake as the sun sets behind trees in the background.

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:

  1. Make sure the battery terminals are clean.
  2. First, connect the red (positive) cable to the red terminal. Then connect the black (negative) cable to the black terminal.
  3. Plug in the charger. Turn it on.
  4. 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.
  5. 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!