How To Charge a Marine Battery

Charging Battery
Marine Battery Tips

Charging a marine battery is a quick and simple process. However, it’s important to be aware of the potential pitfalls, some of which could result in damage to your battery that reduces its ability to hold a charge and eventually causes it to fail.

Most marine batteries available today use AGM, or absorbent glass mat technology and require no ongoing maintenance. AGM batteries charge very quickly, requiring only a fraction as much time as traditional lead acid batteries to reach a full charge.

However, they’re also far easier to damage. Overcharge your AGM marine battery, and there’s a serious risk of it becoming permanently damaged and, as time goes on, useless as a source of energy for your boat or trolling motor.

As the saying goes, “more batteries are murdered than die naturally.” Luckily, it’s easy to prevent damage to your starter, dual purpose or deep cycle batteries by learning how to charge them the right way.

Before you start, check the battery

Since Marine batteries are usually mounted in dark, hard-to-reach positions within your boat, it’s very common for them to pick up dirt and debris over time. This makes it important to check and clean your battery before you start charging it.

First, locate the battery within your boat. Once you remove the battery box from the location in which it’s stored, locate the battery switch and move it to the “off” position. This will ensure you stay safe throughout the checking, cleaning and charging process.

Take the lid off the battery box and check the battery’s terminals and connections. If there is any visible dirt or corrosion on the terminals, the battery might be due for a cleaning. It’s important to clean your battery regularly, as corrosion can prevent it from properly discharging energy.

Connecting the charger to the battery

If the battery is clean and free of corrosion, you can start the charging process. The first step is to connect the battery charger to the terminals of the marine battery. Before we get into this, it’s important to understand the type of charger you should use to charge your battery.

The best chargers for marine dual purpose and deep cycle batteries are smart chargers. Also known as “multi-stage chargers,” these types of chargers are designed to charge your battery according to its temperature and chemistry.

Plug a “dumb” charger into the battery, and it will charge, but with some risk of lasting damage to the battery that can affect its lifespan.

Plug a smart charter into the battery, and it will deliver energy to the battery in three phases — a bulk phase, acceptance phase, and float phase — to maximize the charge and prevent any damage to the battery’s internal components.

If you don’t have a smart charger, we highly recommend purchasing one. Not only does it cost very little money (high-quality chargers are available for $50 to $100), but it will also extend the life of your marine battery.

Charging the battery

Assuming you have the right type of charger, the next step is to connect the charger clips to the battery’s terminals. Once they’re connected, switch on the battery charger and allow the battery to charge.

If your charger has adjustable charging settings, it’s important to read both its manual and your battery’s charging manual before you begin charging. This will help you work out the best speed for effectively charging your battery.

From this point on, the charger will manage the entire process. If you have a smart charger, you can check the LED display to see your battery’s charging percentage. The charger will adjust its charging method as it moves through the bulk, acceptance and float phases.

By using a smart charger, you prevent any risk of damaging the battery due to overcharging. As such, we highly recommend replacing your old charger (if you use a non-smart charger) before you begin charging your marine battery.

Removing the Charger

Once the battery is fully charged, switch the charger off and remove the charging clips from the battery terminals. Place the top cover back onto the battery box and move the battery back into its original position.

That’s it — you’re done! Once you’ve fully charged your marine battery, it’s time to go out on your boat and enjoy yourself. If you have a second battery on board your boat, just repeat the process above to bring it to a full charge.

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