Marine batteries are made specifically for use on boats and feature thicker plates and sturdy construction to withstand the vibration and pounding that can happen on any powerboat. The fact that marine batteries are typically more expensive than car batteries may tempt some boat owners to buy an auto battery rather than a marine battery. Don't choose that bad option. An auto battery in a boat won't last as long or be as dependable as a marine battery.
Types of Marine Batteries
There are three basic types of marine batteries:
A separate deep cycle "house" battery should be used for any electric trolling motors, thrusters, windlasses, or other battery-operated accessories that consume more current. Only applications with frequent high rates of discharging and recharging should use deep cycle batteries. A deep cycle battery has thicker, heavier plates than a cranking battery and is built differently. Trolling motors and windlasses, for instance, have longer, higher amperage requirements that would heat and distort a cranking battery's thinner plates.
The purpose of the cranking battery, which has more but thinner plates to provide a quick voltage spike for starting an engine, is not to sustain high power output for extended periods of time. Although a two- or three-battery system is highly advised to separate the engine battery from the accessory (house) batteries, a deep cycle battery can be used to start your motor in an emergency.
Having your battery "load tested" is the best way to ensure that it is still in good condition. The majority of auto parts or battery specialists will load test your battery free of charge and let you know if it's still in good condition. Even if something has died once or twice, it might still be useful. As something other than the battery itself may be the root of the issue, the rest of your electrical and charging systems may also need some attention.
Replacing Your Boat's Battery
When changing a marine battery, refer to your boat's owner's manual or a marine dealer, and make sure the new battery you purchase is appropriate for your boat. Reverse capacity, marine cranking amps, and ampere hours are used to rate marine batteries. The reserve capacity and ampere hour rating are the two factors you should focus on when buying a deep cycle battery. Pay special attention to the marine cranking amps when choosing starting batteries. When looking for a dual-purpose battery, look at all three rankings.
If you add electrical equipment to your boat, you might need to upgrade to a battery with a higher amp-hour rating, particularly if you spend a lot of time trolling with the engine running at a very low speed (which means the alternator gets less power to charge the battery) or if you use equipment like the audio system while beached or at anchor.
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