Your batteries turn your starter motor – and run your GPS, radio, and fish-finder. But chances are, they’ve been lying unused since you winterized your boat. So how do you de-winterize your batteries – and make sure they deliver maximum performance and service life?
Step 1: Consult your boat owner's manual
Your owner’s manual will help ensure everything runs smoothly – and lay out the steps before and after you prepare your battery.
Step 2: Top off battery cells with purified water
(flooded lead batteries only)
Ensure that the plates of the battery are covered by distilled or deionized water. Filling the batteries too high prior to chagrining could result in overflow. Do not use tap water; trace minerals can harm batteries plates.
Step 3: Clean battery components
Before cleaning batteries, take these safety precautions:
- Wear protective glasses, gloves, and old clothes (including a long-sleeve shirt)
- Keep rinsing water nearby in case of spills
- Take off all jewelry, watches, etc. and remove electronics
- Consult Crown Battery’s “Safety First” guide for more maintenance guidelines
Next, clean the batteries:
- Clean battery terminals, cable terminals, and case with a baking soda paste and a terminal brush. This neutralizes acid and prevents conductivity between the terminals.
- Once connections are made, coat battery terminals with insulating, non-conductive grease or spray-on protective film. (This helps prevent performance-sapping corrosion.)
Step 4: Measure voltage between battery terminals
Using a digital voltmeter, measure the battery’s voltage. It should read 12.8V (no lower than 11.9V).
If you’ve just charged your batteries, wait several hours before measuring voltage. (In a pinch, briefly apply a load to remove some of the surface charge.)
And consider adding this testing to your regular maintenance routine. Because when bad batteries receive current from good ones, they lower the state of charge and lifespan for good batteries.
Note: Since a voltmeter measures overall state of charge, you’ll need a hydrometer to determine whether individual cells are fully charged. When using a hydrometer, top off and charge batteries before taking measurements. To prevent inaccurate readings: test at ~70°F or use a temperature-compensating hydrometer.
Step 5: Charge batteries fully
(13.4 volts for flooded, 13 volts for AGM batteries)
It’s best to use a smart charger designed for marine batteries. (Never use old-fashioned manual chargers.)
Smart chargers offer numerous benefits over conventional chargers. For instance, they:
- Deliver an optimal charge every time
- Prevent overcharging and overheating – common in older chargers – that shorten lifespan
- Equalize or “float” batteries – that is, deliver a low-level charge to balance cells
Whatever charger you use, run a full cycle, then measure their voltage again. Top off flooded batteries with distilled or deionized water.
If possible, keep batteries in a full charge state between uses and during the off-season. This minimizes self-discharge and sulfation (which reduces chemical reactions necessary for energy storage, and cuts lifespan). Otherwise, charge batteries at least once every month, including off-season.
Step 6: Reinstall batteries as needed
- Record your installation date on the battery with a grease pencil, or in a logbook.
- Tie down batteries tightly using a battery box or bracket. (Double-check to confirm it meets American Boat and Yacht Council specifications.)
- Crimp terminals tightly, then cover with heat-shrink tubing.
- Ensure the positive terminal is covered. Many retailers sell inexpensive “boots” that prevent arcing, sparks, and other hazards that could result from objects like tools falling on batteries.
- Swap out wingnuts for stainless steel lock nuts to ensure tight connections and maximum performance.
If your batteries aren’t operating properly or won’t hold a charge:
These steps will help you find out whether your batteries are repairable or require replacement:
- Flooded batteries: Measure each cell with a hydrometer. Cells in a fully charged battery should read between 1.230 – 1.300, depending on temperature. Any difference greater than 0.050 could indicate a faulty cell.
- You can rent or borrow a load-testing device or other equipment to determine your battery’s health.
- Your battery vendor or an electrician will have additional tools and can help diagnose battery problems.
If your battery is damaged and cannot be equalized back to regular operation:
Make sure it’s recycled (lead batteries are 99% recyclable -- more recyclable than an aluminum can).
Always buy replacement batteries in matching styles and sizes.
Finally, consult North American Clean Energy’s article “ 5 Things to Look For In Your Next Battery” to make sure you select the right battery for your boat.