Battery Storage

Equalization Charge

An equalization charge is a controlled, intentional overcharge applied to flooded lead-acid batteries that raises the charging voltage above the normal absorption level to actively remix the electrolyte and reverse sulfation buildup on the battery plates. It is a maintenance procedure specific to flooded (wet cell) lead-acid batteries.

During normal cycling, the sulfuric acid electrolyte in flooded batteries stratifies — the heavier acid concentrates at the bottom while the lighter water rises to the top. This stratification causes uneven plate reactions and accelerates degradation. The vigorous gassing produced during equalization physically stirs the electrolyte, restoring a uniform acid concentration throughout the cell.

Equalization also targets sulfation — the buildup of lead sulfate crystals on the plates that occurs naturally during discharge. These crystals harden over time if not dissolved. The elevated equalization voltage drives a stronger charging current that can break down soft sulfation and restore capacity that would otherwise be permanently lost.

A typical equalization charge raises voltage to 15.0-16.0V for a 12V battery bank (2.5-2.67V per cell) for 1-3 hours, depending on the battery manufacturer's specification. This is significantly above the normal absorption voltage of 14.4-14.8V and must be timed carefully to avoid excessive water loss or plate damage.

Equalization should never be applied to sealed batteries (AGM or gel) — the elevated voltage produces gas that cannot be vented, potentially causing swelling, cracking, or rupture. It is also unnecessary for LiFePO4 batteries, which use an entirely different chemistry and have BMS-controlled cell balancing instead.

Frequently Asked Questions

How often should I equalize my batteries?

Most flooded lead-acid battery manufacturers recommend equalization every 30-90 days, or whenever specific gravity readings between cells differ by more than 0.015 points. Some charge controllers can be programmed to run automatic equalization cycles on a schedule. Always check your battery manufacturer's specific recommendations.

Can equalization damage my batteries?

If done correctly per the manufacturer's specs, equalization extends battery life. Done incorrectly — too high voltage, too long duration, or applied to sealed (AGM/gel) batteries — it can cause permanent damage. Never equalize sealed lead-acid batteries or lithium batteries.