Equalizing Charge

Basic Definition

An equalizing charge is generally performed as a part of periodic battery maintenance.  It is generally a procedure that is applied to serviceable flooded lead acid batteries and fundamentally involves overcharging the batteries.

Purpose of Equalizing Charge

The intent of this charging procedure is to remove sulfation that formed as a result of the batteries being undercharged.

Another objective is to bring all cells to an equal state of charge. A battery that does not receive a periodic equalizing charge will have cells that are increasingly out of balance.  This condition of imbalance is in fact what causes one cell within a battery to become overcharged while another becomes undercharged.

Equalizing Charge Procedure

While the specifics of applying this charge can significantly from manufacturer to manufacturer, the fundamental steps are generally the same.

First, the battery is brought to a full state of charge.

Second, the battery specific gravity is measured.  If the difference is greater than 0.030, an equalizing charge is applied.

The charge voltage applied is nominally 2.5 volts per cell, or 15 volts for a twelve volt battery.

The charging time is a parameter that will vary from manufacturer to manufacture.

That said, a more generic method can be applied.  Specifically, one applies the equalizing charge and checks the specific gravity every hour until they cell measurements have equalized.

The frequency of the equalizing charge is something that each battery manufacturer differs on.  For example, some will recommend be applied every month or every ten cycles, while another will recommend every six months or every 20 cycles.

Applying an Equalizing to VRLA batteries.

Balancing AGM or Gel batteries with an overcharge is not something a lot of battery manufacturers recommend.  This is partly due to the fact that you cannot check the specific gravity of the electrolyte.

Further, the nature of the equalization is one where some electrolyte will likely be boiled off.  Being sealed batteries, it is impossible to refill the electrolyte with distilled water.

While this could be a point of concern about AGM and Gel batteries, it is important to note that the manufacturing deviations between cells (that cause imbalance) are not as great in the VRLA as they are the serviceable flooded lead acid battery.

That said, people can and do apply equalizing charges to AGM and Gel batteries.   People doing such a thing are either ignorant or have developed a pretty good “feel” for performing this maintenance step.