Last modified on March 9, 2020

Equalization is a process of controlled battery over-charging. It is used as a routine maintenance activity and a remedial activity for flooded lead acid batteries. It is part of the multi-stage charging process.

Lead acid batteries suffer from ‘sulfation’. This happens when the sulfuric acid inside the battery cells form tiny crystals on the lead battery plates, thus blocking that part of the plate and reducing battery capacity and performance.

Over time and depending on the conditions of use, lead acid batteries can become very sulfated and operate at only a fraction of their rated capacity.

To avoid this, a flooded lead acid battery bank should be equalized on a regular basis. The optimal frequency of equalization will depend on several factors, but most seasonal cottages should be equalized a couple times per year and full time homes ~4 times per year.

Many solar charge controllers have the ability to auto-equalize; this is a good option and we recommend auto-equalizing for a short duration (ie 1 hour) every 30 to 60 days. Consult your charge controller and battery manuals for more details.

A well designed system should be able to equalize from solar only, but depending on the season and other house loads you may need to run solar + generator to get a good equalization.

When a battery bank becomes heavily sulfated it needs aggressive equalization. This is called ‘corrective equalization’. Corrective equalization involves charging the battery bank with a very high voltage, much higher than it would see in normal operation or even during routine equalization. The battery bank will get hot and it must be actively monitored to ensure that it does not exceed safe operating temperature. Doing so could permanently damage the batteries. A very heavily sulfated bank may required multiple corrective equalization cycles.

All equalization will be accompanied by the production of battery gasses. A flooded lead acid battery bank should have active ventilation to the outdoors to prevent those battery gasses from accumulating inside.