First, avoid automotive batteries and stick to marine batteries. A marine battery’s construction is more durable, using more plates that are more ruggedly secured in a more rugged case. A marine battery’s threaded posts help ensure that cables don’t come loose with vibration like they might with conventional battery posts.
Even within the broad category of marine batteries, there are things to look for. Investigate the internal construction of the battery. For instance, batteries using more thin plates and pure lead (called TPPL batteries) often fare better than traditional flooded batteries, which use fewer, thicker plates, and absorbed glass mat (AGM) batteries, which utilize oxides made of larger grains than pure lead and which may corrode more easily. The finer-grained, pure lead used in TPPL batteries makes them less prone to what is called “shedding’’ of the materials from the plates due to a boat’s pounding across the water. These features also allow TPPL batteries to fit more plates because each plate is thinner, which ups a TPPL battery’s electrical performance, especially for the burst of power required for engine starting. But internal ruggedness, specifically a more durable grid, and more advanced internal design aren’t the only advantages TPPL batteries offer over flooded-cell and AGM batteries.
When shopping, compare the output of different batteries using two basic specs. One, the “starting power” is in cranking amps, listed as either cold cranking amps ( CCA) or marine cranking amps (MCA), bearing in mind that CCA is rated at 0 degrees F and MCA is rated at 32 degrees F. The second, which might be thought of as “staying power,” is officially known as reserve capacity, usually listed as the number of minutes it can be run at 25-amp draw before discharge. When comparing, make sure you are using the same rating and same measurements because different makers will highlight different specs.
Here is where you’ll discover that TPPL batteries offer excellent performance as both deep-cycle and starting batteries. This is a result of a TPPL’s utilizing more and thinner plates in each cell. Of course, it’s safe to say that a majority of boaters need a dual-purpose type of battery/batteries aboard their boats.
Boats get used sporadically, so boaters need batteries that don’t self-discharge at a great rate. Flooded batteries do so most rapidly, while AGM and TPPL batteries self-discharge at much lower rates, making them a better choice.
Another factor to consider is the depth of discharge. Basically, the deeper you discharge a battery on a regular basis, the shorter its life will be. Battery technology plays a big part: Flooded batteries do not withstand such “deep cycling” as well as AGM batteries, which, in turn, are often surpassed by the deep-cycle ability of TPPL batteries. So ask for a marine battery’s cycle-life specs, consider the technology, and then weigh the benefit versus cost.
Making smart battery-buying decisions ensures happier boating.