Equalizing charge is overcharging a flooded lead acid battery to counter sulfation and stratification. Sulfation is the process of accumulation of sulfate crystals at the lead plates when the battery is constantly undercharged. This has been discussed in detail in a previous post (Battery Sulfation). Stratification is accumulation of acid at the bottom of the cell when the battery has not been used for a long time. Sulfation and Stratification lead to decreased battery capacity and longevity. So taking care to prevent their occurrence by applying equalizing charge is very important.
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.
Manufacturers recommend equalizing the battery once every six months if the battery is not used much. Or, equalizing charge should be applied after 20 cycles. If you are a methodical person you can also take specific gravity measurements using hydrometer and decide accordingly. You can learn all about taking specific gravity measurements in this post about testing a battery. If the specific gravity of the cells varies by 0.03 or more, you should apply equalization charge.
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Now, specific gravity measurements can be taken for flooded lead acid batteries only. So equalizing charge is ideally suited for such batteries only. However, for VRLA and other sealed batteries you can accept the manufacturer’s recommendation and apply equalization charge accordingly.
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