Boat battery care

My boat’s safety depends on its batteries being able to start the diesel engine and run the boat’s systems and instruments. Proper boat battery care ensures that they’ll be ready when I need them.

My boat has two batteries with a switch to turn on one battery, two or none. One is a starting (cranking) battery. The second is a deep cycle (marine) battery, which has less instant energy but thicker plates so it can withstand a number of discharge cycles.

How batteries die

If you take good care of your batteries, they should last you at least four years. Eighty percent of all battery failure is related to sulfation build-up, which occurs when sulfur molecules in the acid discharge onto the plates. When this happens, the lead plates become coated, and the battery dies. Here are a few things that can cause sulfation and shorten your battery’s life:

sitting too long
dirty or loose battery cables
storing without power
undercharging
letting the electrolyte level get too low, exposing the plates to air
sitting in extreme heat (over 100 degrees Fahrenheit)
cold weather, which slows down the chemical reaction and provides less energy
being drained without being charged (A short or running electrical equipment, such as an automatic bilge pump, could discharge a battery completely.)

Preserving your battery

Battery charging is important. Energy must be put back, and the sooner, the better. Your engine’s alternator is a battery charger, but be aware that it can overcharge. While I tend to charge the batteries before taking the boat out, it would be wiser to charge them upon returning to the dock. This would leave the battery fully charged and ready for the next outing.

Check your batteries’ age. (The month and year of manufacture should be printed on them.) You can check the specific gravity with a hydrometer and the output with a voltmeter. Compare these numbers to those recommended for your battery.

If a new battery is in order, determine the type you need. Starting batteries should have the highest reserve capacity available. Deep cycle batteries should have the greatest amp hour rating available.

Make sure that the battery type and size are appropriate for your boat and that the terminals match your boat’s cable hookup.

Lastly, make sure to buy a fresh battery. Check the date to see how long it has been sitting on the shelf. –Rex Allen Holden