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The term, "equalization", when applied to storage batteries refers to a process whereby you intentially provoke an "over-voltage" charging condition for a fixed period of time. This tends to produce bubbling sufficient to stir up the electrolyte. It helps also to knock loose PbSO4 crystals off the plates, thereby increasing battery capacity previously lost. And, of course, it tends to "equalize" the specific gravity of each individual cell in the battery or battery bank. Hence, it's name.
For a 12V system, an equalization charge is about 15.5-16.0 volts for several hours. Consult your battery manufacturer for specifics. Trojan batteries have a white paper available which provides good information.
Some AGMs can be equalized, too. See the manufacturer's recommendations.
Gelled batteries are not normally equalized, since they are quite voltage sensitive, and high voltage can damage them permanently.
As the previous post said, some modern battery chargers have an equalization cycle, either manual or automatic. Also, some smart regulators, like the Balmar MC-612, have an equalization setting (manual) so you can equalize your batteries using the engine's alternator.
Batteries should be inspected carefully before equalizing to be sure their electrolyte levels are sufficient. If you have HydroCaps, these need to be removed before equalizing. WaterMiser caps can be left in place.
Sensitive electronic equipment should be turned off during the equalization phase, since voltages can be considerably higher than they were designed for.
Last edited by btrayfors; 12-30-2008 at 11:13 AM.