There are up to four phases of battery charging-bulk, absorption, equalization and float. The bulk stage is where the charger current is constant and the battery voltage increases.
You can give the battery whatever current it will accept not to exceed 20% of the ampere-hour rating and this will not cause overheating. T
he absorption phase is where the charger voltage is constant and current decreases until the battery is fully charged.
This normally occurs when the charging current drops off to 1% or less of the ampere-hour capacity of the battery. For example, the ending current for a 100 ampere-hour battery is 1.0 amp or less.
The optional equalizing phase is a controlled 5% overcharge, which equalizes and balances the voltage and specific gravity in each cell, the effect of increasing the charge voltage.
Equalizing reverses the build-up of chemical effects like stratification, where acid concentration is greater in the bottom of the battery. It also helps remove sulfate crystals that might have built up on the plates.
The frequency recommendation varies by manufacturer from once a month to once a year, from 10 to 100 deep cycles, or when a specific gravity difference between cells reaches .03. To equalize, fully recharge the battery; next, increase the charging voltage to the manufacturer’s recommendations (if you cannot find one, ADD 5%).
Heavy gassing should start occurring (be VERY CAREFUL about safety precautions). Take specific gravity readings in each cell once per hour. Equalization has occurred once the specific gravity values no longer rise during the gassing stage.
The optional float phase is where the charge voltage is reduced, held constant and used indefinitely to maintain a fully charged battery.