Battery Equalization

October 24, 2005
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Much of this discussion about equalization has been taken from the book Living on 12 Volts with Ample Power. The book contains much more about equalization and should be consulted if questions remain.


Battery equalization is a potentially dangerous operation which can result in explosive damage to the battery with collateral damage to anything or person in the vicinity. Batteries contain sulphuric acid which is corrosive, burns skin, and can be blinding on contact with the eyes. Wear eye protection at all times.

What is Equalization?

Liquid electrolyte batteries that have been floated at a low voltage for long periods need to be periodically equalized. Equalization is the process that equalizes the specific gravity in all the cells. Basically, equalization amounts to a controlled overcharge.

Some, maybe all, Absorbed Glass Matte, (AGM), batteries may also need periodic equalization. Consult the manufacturer for specific guidelines.

Current Limiting Required

To equalize a battery, you need a charge source which can be current limited, such as the Ample Power Smart Alternator Regulator. Set the current limit at 3-7% of the Amp-hour rating of the battery. That is, for a 100 Amp-hour battery set the current limit at 3-7 Amps. Apply that current to the battery for about 4 hours, or until the battery voltage rises to 16.2 Volts for liquid electrolyte batteries or 15.5 Volts for AGM batteries. The Smart Alternator Regulator can equalize batteries automatically.

Fully Charge

Before equalization, fully charge the batteries and let them reach the float voltage.

Turn Off Voltage Sensitive Loads

Since the battery voltage rises to beyond normal operating values, be sure to turn off all loads which are voltage sensitive.

Battery temperature should also be observed during the process to prevent overheating. A battery being equalized can go into thermal runaway where the build-up of heat aggravates the conditions which generate heat ...a vicious feedback which may end with an explosion.

Pre-adjust the Current Limit

Before starting the equalization process, adjust the current limit to zero. On a Smart Alternator Regulator, this means turning the adjustment potentiometer up to 20 turns counter-clockwise.

Adjust Engine RPM

If you're using an engine to equalize, then the engine RPM must be fixed at a constant value and remain there during the equalization process.

Start the Equalization Cycle

Enable the equalization cycle to start. Now, very slowly, adjust the current limit potentiometer to 3-7% of battery capacity. That is, measure battery current and adjust the potentiometer until that current is 3-7% of the nominal Amp-hour capacity of the battery.

Monitor, Monitor, Monitor

Continue to monitor battery current, battery voltage and battery temperature. Current should stay relatively constant, and there should be a steady rise in battery voltage.

Keep a close eye on battery temperature. In no case should it exceed $115^\circ $ F, ($46^\circ $ C).

Terminate the Cycle

Terminate the process after 4.5 hours, or when battery voltage rises to the limit. If an automatic device is being used, make sure it completes the process and resets to a normal regulation setpoint.

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