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Pre-Season Battery Inspection and Maintenance

Battery maintenance

Most of us have had a long wait to meet our boats and understandably we are all impatient to leave the dock as soon as possible. But don’t forget, patience is a very important aspect of good seamanship. So, don’t push your boat away from the dock until she is fully ready!

Batteries by nature do not really like standing idle for long. Because of that, battery testing and maintenance should be one of the high priority items in your season preparation list. Otherwise, neglected batteries may give you a frustrating surprise when least expected.

Pre-season battery testing and maintenance can be done in 3 east steps.

  • Inspection
  • Testing
  • Cleaning and Maintenance

Don’t forget, when you are dealing with the batteries, you will be dealing with the electricity, chemicals (incl. Acid) and tools. Before you take steps to inspect and maintain your batteries, you need to use proper protection gear (goggles, gloves, etc) and remove all metal jewelry such as rings, bracelets, etc. Do not forget that your work area has to be well ventilated and illuminated.


Below is a list of basic items (you may use other proper equipment to do the job)

  • Goggles & Gloves
  • Baking Soda
  • Distilled Water *
  • Hydrometer *
  • Vaseline
  • Multimeter

* if you are using Flooded Lead-Acid Batteries (FLA)

Corroded terminal

1. Start with a visual check of the battery.

  • Look for cracks in the container.
  • The top of the battery, posts, and connections should be clean, free of dirt, fluids, and corrosion. If any of the above exist, do a proper cleaning according to recommendations in section
  • Replace any damaged batteries. (Cracked battery containers may be repaired as well. But I personally do avoid repairs and replace them if possible)

2. Check for fluids (or leak marks) on or around the battery. This may be an indicator of electrolyte spill, leach, or leak. Leaking batteries must be replaced (or repaired)

3. Check all battery cables and their connections.

  • Look closely for loose or damaged parts including terminal posts and cable connectors.
  • Battery cables should be intact; broken or frayed cables can be extremely hazardous.
  • Replace any cable that looks suspicious.

Both open-circuit voltage and specific gravity readings can give a good indication of the battery’s condition and health. Routine voltage and gravity checks will help to spot the signs of improper care, such as undercharging and over-watering, and possibly even locate a bad or weak battery.

Specific gravity tests can tell you a lot about your FLA Flooded Lead-Acid Batteries and it is a little more complicated compared to open-circuit voltage tests. Considering the depth of the subject and decreasing popularity of the FLA batteries, I will cover specific gravity tests in a separate blog article soon.

multimeter voltage reading

Open-Circuit Voltage Test
An important point that you should plan ahead before you perform an open-circuit voltage test. For accurate readings, batteries must remain idle (no charging, no discharging) for 24 hours ideally. (or 6 hours minimum)

  • 1. Disconnect all loads from the batteries. (I usually disconnect the negative terminal before I start)
  • Measure the voltage using a DC voltmeter.
  • Record your readings with the number/identifier of the battery under test.

Evaluate your readings. Here’s a simple table for 12V Batteries:

State of ChargeVoltage
100 %12.7 V +
75 %12.4 V
50 %12.2 V
25 %12.0 V

If your battery is:

  • Reading 0 volts, chances are the battery experienced a short circuit
  • Cannot reach higher than 10.5 volts when being charged, then the battery has a dead cell
  • Fully charged (according to the battery charger) but the voltage is 12.4 or less, the battery is sulfated

Sulfation is the process of accumulation of sulfate crystals at the plates when the battery is constantly undercharged. Naturally, re-charging the battery will reverse the sulfation crystals. But if the battery left as, under-charged or drained for extended periods of time, the sulfation will increase.

Sulfation decreases the battery’s potential to reach to a full charge, and it causes faster than normal self-discharge. An equalization charge may reverse the sulfation. Equalizing a battery is done by applying a 10% higher voltage than the recommended charge voltage. This high level of charge frees the sulfur ions back into the electrolyte and desulfates it. The high voltage also forces the acid accumulated at the bottom of the cell to rise up and mix equally with the water. Thus, stratification problem is also reversed.

If your battery charger has the option , you can try to reverse the sulfation by applying an equalization charge. If your readings do not improve after the equalization, replace the sulfated battery.


Batteries seem to attract dust, dirt, and grime. Keeping them clean will help to spot problem areas when they appear and avoid problems associated with the grime.

Battery Box installation
  • Check that all vent caps are tightly in place. (for FLA batteries)
  • Clean the battery top with a cloth or brush and a solution of baking soda and water.
  • Rinse with water and dry with a clean cloth.
  • Clean battery terminals and the inside of cable clamps using baking soda or post and clamp cleaner.
  • Reconnect the clamps to the terminals and thinly coat them with vaseline or anti-corrosive spray or silicone gel.
  • Tighten all wiring connections to the proper torque (based on the battery manufacturer’s recommendation). Do not overtighten terminals. Overtightening can result in post breakage, post meltdown, or fire. Make certain there is good contact with the terminal
  • Keep the area around batteries clean and dry.
  • Batteries must be tied down properly. You can use various proper fasteners to do this job such as a box or bracket with threaded rod and nuts or webbing straps. According to American Boat and Yacht Council (ABYC) standards the batteries should resist 75 pounds of force in different directions.

One more tip;

– I always number each battery in my battery banks and write the date of installation on each battery. Use a permanent marker in case the manufacturer label on the battery couldn’t survive the boat conditions.

Have a safe and happy sailing season.


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