Battery Choices

How to choose batteries for starting and household needs
There are two main classes of electrical storage batteries for pleasure boats: unsealed and sealed. And there are two main applications: cranking and deep cycling.Unsealed (or “flooded”) lead-acid batteries, the oldest design, operate at atmospheric pressure. They have vent caps open to the air to allow hydrogen and oxygen gases to escape during the charging process. However, because the electrolyte is allowed to “boil away” in this manner, it must be topped off occasionally with distilled water.Sealed batteries don’t allow the electrolyte to escape. They force the gases to recombine, so there is no maintenance to be done. The electrolyte in most sealed batteries is a gel rather than a liquid.Starting batteries are designed to release a lot of current over a short period. They need to be recharged immediately after use and they will be damaged if they are deeply discharged. They are excellent for supplying power to the starter motor that brings a boat’s engine to life.

Gel-cell batteries are sealed, need no maintenance, and will not spill acid if tilted. They make good deep-cycling banks

Deep-cycle batteries are designed to deliver current at a lower rate for a much longer period. They may be deeply discharged hundreds of times without damage. They are excellent at supplying the long-term household needs of a boat, but they cannot supply the same huge surge of current to the starter motor that a special starting battery can.A new generation of batteries tends to blur the distinctions of the various types, combining all the best features. Absorbed glass mat (AGM) batteries are similar to gel batteries, but are not damaged by high charging voltages, as the older gel cells were. Manufacturers claim that they have a high discharge capability but will also withstand deep discharge as well as flooded batteries can. In short, they eliminate the need for two different kinds of battery on board. Some of the batteries manufactured with this new technology are spiral-wrapped, and look like jelly rolls stood on end. They are, of course, more expensive than flooded batteries.Time will tell how effective and economical AGM batteries are. If you’re not willing to experiment, and especially if you’re not averse to a little maintenance now and then, the safest bet is still the flooded lead-acid battery in starter or deep-cycle form. For the latter, 6-volt golf cart batteries, linked together for a 12-volt system, will take a lot of abuse and are still an excellent choice.See also Amp-Hour Ratings; Battery Needs; Checking a Battery; Cranking Ratings; Locating Batteries..

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