It’s time for new batteries, but you’re not sure if you should go with flooded-cell, gel or AGM (absorbed glass mat). Each type has pros and cons.
Flooded-cell batteries are less expensive, are less likely to be damaged by overcharging, and will last longer than the other types if they’re properly maintained. Check the electrolyte levels periodically and see to it that the batteries are ventilated well. On the downside, you have to worry about possible battery acid spills. Be sure your wet cells are immobile.
AGM batteries are completely sealed and pose no acid-spill threat, and they require no maintenance. AGM batteries are more expensive than flooded-cell batteries, but they boast better shock and vibration resistance. They have a higher recharge acceptance rate than either flooded-cell or gel batteries, so they can be recharged at a higher rate without damage, says Ed Sherman, the American Boat & Yacht Council’s director of educational programming and delivery.
They weigh more than flooded-cell types, but “AGMs will typically pack more amp hours into a case of the same size as its gel or flooded cousins,” Sherman says. “In the end, the actual available amp hours per pound and real estate used on the boat will diminish the weight issue.”
Gel batteries are also sealed and require no maintenance. They resist damage caused by overcharging. Another positive is their low discharge rates, which allow them to be stored untouched for long periods.
But they do need TLC when it comes to recharging. They must be recharged between 13.8 and 14.1 volts, and they require a battery charger with a gel setting. At charging voltages above 14.2, gas bubbles can form in the electrolyte gel and permanently damage the battery, says Dave Laska, owner of L&L Electronics in Branford, Conn.
Adds Sherman: “Voltage regulators from most manufacturers are factory-set to 14.8 volts, and that is too high for the gel cells. So, on a powerboat, every minute you are running the engine alternator you are, in effect, damaging a gel battery.”
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This article originally appeared in the December 2011 issue.