It's important to choose the right marine battery regardless of the type of boat you have. A marine battery provides direct and backup power to a boat, and for overnight stays, having one that powers all the on-board accessories makes boating more pleasant. Because marine batteries come in such a variety of sizes and charges, you must know what to look for. Follow a few simple guidelines, and you'll be able to purchase a marine battery that fits your needs.
Determine if you need a "starting" battery or a "power" battery. Starting batteries help with sudden electrical demands such as starting an engine. Power batteries provide ongoing power to boat appliances.
Review the warranty. Some marine batteries are meant for five seasons, but the warranties only extend for two seasons. Check to see if the warranty is "full" or "pro-rated." Full warranties provide a replacement battery if your battery fails within the warranty period. Pro-rated warranties provide a pro-rated refund or credit for the unused portion of the warranty.
Determine if you need a "wet-cell" or AGM battery. Wet-cell batteries have individual cells that must be replenished with water. They last a long time and cost less, but they release dangerous gases, so they must be properly ventilated. AGM batteries cost more, and are more massive, requiring a few extra inches of installation space. AGM batteries, however, have solid-cores, so they do not require replenishment and do not vent dangerous gases.
Determine how many volts you need. Twelve volts provides adequate power to most small boats in mild temperatures. For colder weather or for larger engines, multiple 12-volt batteries, or single batteries capable of 18 or 24 volts, might be required.
Determine the installation requirements. For instance, some boats have flat battery cases that can accommodate either wet-cell or AGM batteries. Other boats have inclined battery compartments which can only house AGM batteries.
Make sure the size of the battery will fit in your boat.
Determine the cold-starting amperage. Cold-starting amperage is how much amperage a battery can deliver for up to 30 seconds when the outside temperature is zero degrees F without allowing the battery to fall below a certain voltage. Average cold-starting amperage is 550, which maintains batteries at 10 volts. Batteries with cold-starting amperage between 300 and 500 let the voltage fall to 7.2 volts, which is the least voltage necessary to ensure a boat has enough starting power. If you plan on starting your boat in cold weather, you want a battery with a minimum of 550 cold-starting amps.
Determine the reserve capacity. The reserve capacity is how many minutes a brand-new battery will deliver a continuous charge at 80 degrees F. High-quality batteries have reserve capacities upwards of 180 minutes; low-quality batteries have reserve capacity ratings of around 35 minutes. The average marine battery reserve capacity should be between 60 and 90 minutes.
Determine if the battery fits your budget. Shop around, as many batteries are expensive, and even a modest 10 percent savings could save you up to $25.