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VOL. 9 NO. 11
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Battery basics

How to take care of your boat’s batteries

Battery basics

My boat’s safety depends on its batteries being able to start the diesel engine and run the boat’s systems and instruments.

I have two batteries on my boat 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.

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. The lead plates become coated, and the battery dies. Here are a few things that can cause sulfation and shorten your battery’s life:

  • The battery sits too long.
  • The battery cables aren’t clean or tight.
  • The battery is stored without energy input.
  • The battery is undercharged.
  • The battery is not checked, and the electrolyte level gets too low, exposing the plates to air.
  • The battery sits in extreme heat (over 100 degrees Fahrenheit).
  • Cold weather is hard on a battery. The chemical reaction slows down and provides less energy.
  • The battery has a drain on it while not being charged. If there is a short or electrical equipment running, such as an automatic bilge pump, a battery could discharge completely.

Battery charging is important. Energy must be put back, and the sooner, the better. The alternator in your engine 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 the age of your batteries (the month and year of manufacture should be printed on them). You can check 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 needed. 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.
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