Dear Boat Doctor,

I need to replace the batteries in my house bank. They are about 6 years old and just don’t seem to hold a charge as long as they used to. But how do I know what type to buy?

Tom Garrison, Charleston, South Carolina

Dear Tom,

When you are replacing batteries, it is good to look to maximize the amount of amp-hours the batteries provide and to minimize the cost. 

You can choose between wet cell, absorbed glass mat and gel batteries. Wet cells are the basic batteries we’ve had for years, with the lowest cost but the smallest charge capacity. They need to be maintained and topped off with distilled water from time to time. 

AGM batteries are similar to wet cells, except electrolyte is saturated into a fiberglass mat and the battery is sealed. They are a little more expensive than wet cell and offer a larger charge capacity.

Gel batteries are also similar to wet cells; the electrolyte has been chemically gelled and the battery is sealed just like an AGM. Gel batteries are the most expensive but give the best charge capacity. You do need to be careful that all of your charging equipment is configured to support gel batteries, if you charge them incorrectly they won’t last long.

For most marine uses, I think AGM batteries give the best performance at the right price.