Upgrading batteries
Ocean Navigator|November - December 2020
Treating batteries as a system works best

For a very long time, high-capacity battery technology remained pretty simple. Wet cell lead-acid batteries were pretty much the only choice boaters had. Over the last 10 to 15 years, battery technology has advanced and more choices of battery design and type have developed. All batteries age, and at some point it becomes time to replace them. This is the time many consider upgrading to one of the newer types of batteries. This may seem a simple task at first, but there is more to consider when changing or upgrading batteries than just the batteries themselves. Batteries are part of a system that must work together to be truly efficient.

The battery system

When thinking about batteries for your boat, you must also consider how the batteries are to be used and recharged. Cabling and connecting the batteries to the boat electrical system, as well as how the batteries are mounted and secured, can also impact battery performance. How a battery is recharged has a large effect on the performance and life of a battery. Not all batteries charge at the same rate or voltage. Incorrectly charging a battery can greatly affect performance and shorten its life.

There will often be several charging sources on a boat, each utilizing a different technology. A typical cruising boat will have a battery charger used when connected to shore power or generator. Otherwise, charging is done via an alternator run off the propulsion engine. Solar and wind chargers will also likely be used. Each of these charge sources must be correctly configured to work with the type of battery installed.

How the batteries are installed and wired also affects performance. Batteries installed poorly can suffer from excess heat, making them less efficient and possibly shortening their life. Poor cabling and connections also can reduce performance and life.

How the batteries are used will also influence selecting the right battery type. Engine-starting batteries, for example, are going to be different from a house bank because they each are required to release their energy differently. The starter battery will need to provide bursts of high energy for brief periods of time, while a house battery will release a little energy over a longer period of time. Each of these requires a different internal structure of the battery. If you do a lot of anchoring, the batteries will be subject to deeper cycling than a boat that goes from one marina to another. Where you plan to cruise and the availability of replacement batteries can also affect the choice of battery type.

All these factors should be considered when selecting replacement batteries. It is beyond the scope of this article to fully explain all the types of batteries, along with the pros and cons of each, but it is possible to help understand some of what is available, as well as to grasp that the battery alone is not the only thing to consider.


Charging is key to efficient battery usage. However, it is not as simple as just dumping power back into a battery. How much power can be replaced and at what rate will vary with battery type. To make matters worse, most boats have multiple charge sources requiring each to work with the selected battery type. Most shore chargers will have settings to adjust to a select battery type, with the exception of lithiumion. Engine-driven alternators with built-in regulators are set up for standard wet cell batteries and are not very efficient for deep cycle batteries. Most alternator regulators are designed for simple wet cell starting batteries. Any other type of battery will require the use of an external regulator that can be programed for a particular battery type. This also would apply to solar and wind charge controllers. The better controllers will have settings for different battery types.

If you’re thinking of going with lithium-ion, it is best to consult with the battery manufacturer concerning charge methods. Because lithium-ion batteries can accept a charge so quickly, they have been known to cause overheating and damage to alternators. Some lithium-ion battery makers are now designing built-in charge controllers to work with standard chargers designed for regular batteries. This could help keep the cost down for switching to lithium-ion.

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