Q:BAD BATTERY

Doc, my boat’s batteries are going bad. They are conventional wet-cell marine batteries. They no longer hold a charge. They are only four years old. I have checked for current leaks and found none,

A:Four years is about what I’d tell you to expect from a conventional marine battery. Batteries in boats often fail physically, not chemically. The pounding and vibration cause more material to shed from the plates than what typically happens in an automotive application (cars and trucks have a suspension system). When enough material falls off, it collects in the bottom of the battery case and eventually shorts the cells. This is just one of several reasons I recommend absorbed glass mat (AGM) batteries to most boat owners. They are more physically durable, hold a charge longer, pack more power in the same-size case, and require no checking of electrolyte levels. They do cost more, but I have found boaters can expect eight or more years of service from AGM batteries.

Finally, I’m glad to know you checked for an errant drain on the batteries. For those who do not know how to do so, here is a link to an article that explains it: boatingmag.com/how-to/locating-groundfaults-current-leaks-and-short-circuits. so I know it is the batteries. In fact, I never seem to get more than three or four years out of a battery. What’s going on?

Declan O’Connell Chicago