How To Properly Charge Marine Battery


To avoid losing power while you’re out in the water, you need to make sure that your boat’s battery is fully charged before you leave the docks. It may seem like a simple and straightforward task, but there are actually several boaters who don’t know how to how to charge the marine battery properly, thus shortening their service life and even putting their boat and themselves in hazardous situations. That said, here’s a quick guide on how to charge a boat battery properly so you don’t end up damaging it.

1. Know the Type of Battery You Have

Marine batteries are generally categorized according to their purpose and chemical make-up.

Type of Marine Battery According to Function

  • Starting Battery. Also referred to as the ‘cranking battery’, the starting battery gives that boost of energy to start the engine.
  • Deep Cycle Marine Battery. This provides consistent power through a slow and steady discharge. This battery is what powers the trolling motor, electronic system, and other instruments on board such as navigational drives, marine stereos, and others.
  • Dual Battery. As the name suggests, this battery is capable of performing the purpose of both starting and deep cycle batteries. This is a great option for those who don’t like having two separate batteries.

Types of Marine Battery According to Chemical Make-up

  • Wet Cell Battery. This is the most common type of marine battery and preferred because they are relatively inexpensive and can also last a long time with proper maintenance. However, this battery will need to be stored in an upright position and have minimal exposure to vibrations. They also pose a hazard when charging because they are not sealed.
  • Gel Battery. Compared to wet cell batteries, gel batteries are a much safer option because they are sealed and contain a viscous gel that will not leak even if the casing is compromised. Unfortunately, these batteries tend to be overcharged and don’t last long.
  • AGM Battery. AGM batteries are the most recommended type of marine battery today because of their many advantages. For one, they require little to no maintenance. Second, they charge quickly. However, they’re also easier to damage, and overcharging them will quickly reduce their service life.
  • Lithium-ion Battery. Lithium-ion batteries may seem like the perfect battery setup for many boaters, but they can be really expensive. However, they do have advantages worth considering. For instance, they can achieve a full charge really quickly, reaching 100% charge in as little as one hour. They’re also a space saver since they’re considerably smaller and lighter than other types of batteries.

2. Use the Right Charger

Regardless of the type of battery you have, it is important to use the right type of marine battery charger to avoid damaging your battery and other untoward incidents from happening.

One thing you need to decide on is whether you want a portable charger or an onboard charger.

  • Portable Charger. Portable chargers are easier to transport and move, which may be an important consideration if your batteries are at home or if they are removed from the boat. They are also cheaper than onboard chargers. The problem with portable chargers is that they can be inconvenient to hook-up.
  • Onboard Charger. Onboard chargers are more expensive will need to be permanently installed and wired to the boat. However, they are more convenient to use since all you need to do is to plug it in and that’s it.

Single- vs. Multi-Stage Chargers

Marine battery chargers are also available in single- and multi-stage variants.  For flooded cell batteries, you can use a standard lead-acid charger for quick and easy charging.

If you have a gel or AGM battery, you will need a smart or multi-stage charger. These chargers deliver energy to the battery in three stages: bulk, absorption, and float charge.  This maximizes the charge and prevents any damage to the battery’s internal components. Also, multi-stage chargers are designed for faster and fuller charging which ultimately leads to longer battery life, more useable capacity from your batteries, less electrolyte loss, and very little chance of over-charging and ruining sealed batteries.

3. Check and Clean the Battery

It is important to clean the battery before charging and regularly to avoid corrosion, which in turn prevents the battery from properly discharging power.

To clean the battery, you first need to turn the battery switch to the “Off” position. Then, remove the lid off the battery box. Afterward, inspect the battery and the terminals to determine which parts need cleaning, then proceed with the cleaning process.

4. Charging the Battery

After cleaning the battery, you can now start to charge it. Simply connect the battery charger clips to the battery terminals. Then, turn on the battery charger and allow the battery to charge. If you’re using a smart or multi-stage charger, there should be an LED display that shows that battery’s charging percentage. Check the display from time to time to ensure that you don’t overcharge your boat battery.

5. Remove the Charger

When the battery has reached a full charge, switch off the charger and disconnect the charging clips from the battery terminals. Afterward, place the top cover back onto the battery box and return the battery to its original position.

Mistakes to Avoid when Charging Marine Batteries


It has been said that most batteries don’t die of natural causes; instead, they’re murdered prematurely by incorrect charging practices. When it comes to charging your boat battery, here are some common mistakes you should avoid.

  • By failing to fully recharge marine batteries, they become sulfated. Also, the battery will not charge properly and provide elevated voltage readings. This causes boat owners to think that their battery is fully charged when actually it isn’t.
  • Overcharging boils the electrolytes out of the battery cells and lead to thermal runaway. This results in the battery becoming hotter and hotter, which then poses a serious threat to the safety of the boat and anyone else on it. Although consistent overcharging can damage all types of batteries, it is especially fatal to gel and AGM batteries.
  • Excessive Deep Discharge. Deep discharges shorten a battery’s service life. Experts generally recommend that you charge and discharge your boat battery through the middle range of their capacity. If you’re using flooded batteries, be sure to equalize them periodically.

Safety Precautions

Marine batteries contain chemicals and components that can be hazardous when handled improperly. Here are a few tips to keep in mind to ensure safety while charging your boat battery.

  • Read the battery and battery charger manufacturer’s manual before starting.
  • Choose a well-ventilated place to charge the battery.
  • Wear goggles and gloves when handling batteries.
  • Make sure that the charger is switched off or unplugged before connecting and disconnecting it from the battery.
  • Thaw out frozen batteries before charging.
  • If the battery feels too hot, stop charging and call in an expert and have it checked.

Globo Surf Overview

As can be seen above, charging a boat battery need not be that difficult. However, it is important to learn how to charge a marine battery properly to make sure that the process is safe and will not cause any damage to the battery. Again, the correct procedures on how to charge a boat battery will depend on the type of battery that you have and the charger, so make sure that you go over the manual first to ensure that you’re doing it right. Doing so ensures that your marine battery will last longer and provide you with more boating adventures.

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Globo Surf
My name is David Hamburg. I am an avid water sports fan who enjoys paddle boarding, surfing, scuba diving, and kite surfing. Anything with a board or chance I can get in the water I love! I am such a big fan I decided to start this website to review all my favorite products and some others. Hope you enjoy!