Equalize Batteries


Fleet Web Addresses:

AGM Battery Equalization Procedure:

By Bobby Ward
Vessel Gra’inne
Size IP350
I currently have a house battery bank consisting of 3 Gp-31 and 2 Gp 27’s which provide a calculated battery capacity of approximately 505 amp hours. Part of normal maintenance for the AGM batteries is a process called equalization, which is performed to reduce internal plate sulfation.

Details provided by Lifeline indicate that the equalization process involves "charging" the battery at 15.5 VDC for a 3 hour period. During this process the current acceptance of the battery will slowly drop from 3 – 5 amps to slightly more than .5 amps during the 3 hour equalization period. I’m sure that there are other methods for doing the equalization that are probably acceptable – if in doubt contact Lifeline. The key to the equalization though is maintaining the equalization voltage at 15.5VDC for 3 hours.

Note: The following procedure was utilized because my power supply was not capable of providing a stable regulated source of 15.5VDC at more than 3 amps. Even with the batteries fully charged, each of the GP 27/31 batteries may draw 3 – 5 amps when the equalization process is initiated. So in my case, with 5 individual batteries in the house bank, initial equalization current could easily have exceeded 20 amps.

The first step in this process is to fully charge the batteries using the shore power charger. I normally leave the charger running long enough to maintain the float charge for at least 4 hours before I start the equalization.

I use a regulated DC power supply with an accurate DC Voltmeter and begin the equalization process by setting the open circuit voltage on the power supply to 15.5VDC and then connecting the power leads directly to the terminals on each battery individually (positive lead from battery under equalization is disconnected from the remaining batteries in the house bank during equalization) – Careful with the disconnected cable end, don’t want a short on this puppy!.

My power supply is current limited so that it will not provide more than 3 amps DC. When I initially connect the power supply to the battery being equalized the voltage drops considerably while the current holds steady at 3 amps and then begins to drop off (allowing the voltage to rise back to 15.5VDC) As soon as the voltmeter indicates 15.5 VDC on the power supply I start the 3 hour equalization process. I have to adjust the power supply occasionally to maintain the voltage at 15.5VDC.

The process is repeated on each battery in the battery bank in turn until all of the batteries have been equalized.


Website design by
  F. Hayden Designs, Inc.

Rock Hall Fleet E-mail
Gratitude Yachting Center E-mail
Last modified: April 05, 2006