Battery Charger Buying Guide

You’re also being smart because choosing a multi-bank onboard battery charger over rotating, or attempting to charge multiple batteries simultaneously with a single charger, allows you to apply all the benefits of a modern charger maintainer to each battery according to its own needs. This is likely to prolong the life of each battery and save you money in the long run.

Today’s onboard multiple-bank chargers are smart chargers with built-in microprocessors to control their multi-phase charging and maintenance processes and may also include desulfation and recover functions. They can deliver better battery performance and longer life. They are also likely to allow you to maintain all of your batteries through the off-season unattended automatically so that your boat is ready when you are in the Spring.

What should you look for in a multi-bank onboard battery charger?


How much power do you need? The output you need from a multi-bank system is closely related to the application of each battery. Here’s a quick guide to amperage output for some applications:

o Low Output – (6 amps or below) A low output model may be applicable for maintenance use or any low amp hour battery application.

o Medium Output – (9 – 15 amps) A medium output model would be applicable for medium use or occasional use perhaps only on weekends for a trolling motor.

o High Output – (15 amps or above) A high output model would be used in high amp hour battery applications (150 Ah for example), or any situation where repeated rapid recharging is required.

Be careful when choosing the amperage output based on its description. Vendors and manufacturers usually publish amperage in two ways. One way is to publish the total amps by multiplying the output of each bank times the number of banks. For example, they might publish the output as 40 Amps, but what they are really telling you is that the charger produces 10 Amps output for each bank. The other way and more useful is to publish the output per bank.

. Then multiply that number by 10% to get the amperage needed. In the case of four 105 amp-hour batteries, you would need approximately 10% of 420 amp-hours or 42 amps or about 10 amps per bank for a 4-bank battery charger.

Battery Voltage

Most marine systems are based on 12V or 24V batteries. Make sure the onboard battery charging system you choose can handle your boat’s battery voltages.

Battery Types

Marine batteries serve various purposes on-board your boat ranging from starting to providing electricity for all the primary systems. You are likely to encounter deep cycle, Gel Cel, or AGM batteries in a marine environment.

Gel Cel batteries require a special charging profile that can only be provided by models specifically designed to charge Gel cel batteries. Onboard battery chargers that charge AGM or deep cycle batteries alone are not equipped to properly charge Gel Cel batteries. Make sure you choose a marine model that can handle all the battery types you have.

Smart Chargers

Most modern multi-bank onboard system have integrated microprocessors. These computers run intelligent programs to charge and maintain your batteries unattended without overcharging or damaging your batteries, charger or boat systems.

Many include built-in safety features that protect against reverse polarity and can also monitor battery