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Battery maintenance

by Tom Jones

Batteries need periodic maintenance to maintain their capacity and maximize life. Required maintenance varies by battery type, but some requirements are common to all.

Applicable to all battery types

Periodically remove and clean all connections to battery terminals and clean the terminals themselves. The connections can oxidize over time and this can result in a lower voltage at your appliances. Use an inexpensive cleaning tool available at auto parts stores, a wire brush, or sandpaper.

Keep the top surface of the battery dry and clean. Dirt allowed to accumulate, expecially if it's moist or wet, can result in a small drain on the battery.

Flooded cell lead-acid batteries

Check the water level regularly by removing the caps or plugs in the top of the battery. If you need to add water, use distilled water available at grocery stores. Since the battery contains acid, you should wear eye and hand protection when adding water.

Periodically check the specific gravity of the electrolyte using a hydrometer. This will give an indication of a bad or failing cell.

Flooded wet cell deep cycle batteries will periodically need equalizing (see the Equalizing section below). However, chassis (engine starting) batteries do not require equalizing.

Absorbed Glass Mat (AGM) batteries

Generally, AGM batteries are maintenance free, except for the items listed under "all battery types".

Gel cell batteries

Generally, gel cell batteries are maintenance free, except for the items listed under "all battery types".


Flooded wet cell batteries used in deep cycle applications need periodic equalizing to restore their capacity. Chassis or engine starting batteries do not normally require equalizing. The need for equalizing comes from two phenomena:

  • Over time, deep cycle batteries form sulphates around the plates, which reduces the effective plate area and reduces the capacity of the battery. This becomes evident when the batteries need recharging at an increasing frequency (they don't last as long before needing recharging).
  • The elctrolyte in Deep cycle batteries such as "house" batteries which sit for long periods of time can stratify. i.e. the specific gravity of the elctrolyte varies from top to bottom a cell.

Both of the above phenomena in flooded wet cell deep cycle batteries can be reversed by the process of equalization. This involves applying a controlled over-voltage while limiting the current for a defined period of time (typically several hours). The process is best achieved with an inverter or charger that has a built-in equalization feature. The battery should be fully charged before beginning equalization.

Check the Maintenance items area of our library for a more detailed explanation of battery equalization.

Warning: Check the owners manual for your inverter or charger to determine the correct equalization procedure.