By Samuel Nelson

These winterizing tips will have your batteries ready for action on launch day.

  • Clean battery tops, terminals and connectors. If your batteries are serviceable (removeable covers), top off the cells with distilled or deionized water.
  • Charge the batteries one final time. Charging ensures they’ll completely recharge next season, and greatly reduces the risk of a frozen battery over the winter.
  • Disconnect the negative cable and wait a few hours before checking voltage or specific gravity. Your voltmeter should display 12.6V for a charged battery. This only tells half the story. The only true way to check the health of a lead acid battery is with a hydrometer after charging it to 12.6V. Check each cell; specific gravity should be 1.265 – 1.285. Warning: Battery acid can cause extreme burns and blindness. Wear safety glasses and gloves.
  • Remove batteries and store them in a dry place where they won’t freeze (not on concrete, as that is a heat sink). Ideally, trickle charge them one day per month. This prevents self-discharge and extends lifespan. Fully charged batteries are also less prone to freezing.
  • Confirm that your charger is designed for your battery type. Flooded (lead acid) and AGM (absorbed glass mat) batteries frequently demand different chargers and algorithms. (Note: Smart chargers can help ensure batteries don’t overcharge.)
  • Batteries left in boats should be connected to a float (tender) charger, which will only charge them when they’ve self-discharged below a certain level, whereas a trickle charger continuously emits a small current of electricity regardless of the charge level or if it’s full.
  • Disconnect terminals to remove all electrical loads from your batteries. Electronics have parasitic (“vampire”) loads – small power draws – even if they’re “off.” This slow drain, combined with battery self-discharge, is enough to damage batteries in the off-season.

Samuel Nelson is the Principal of Nautical Circuits, LLC, a marine electrician in Avon, CT. Call 860-305-3939 or visit