Absorption charging is normally the second state in a multistage charging process. The absorption charge normally applies what is known as a topping charge.
Absorption charging is also known as constant voltage charging.
In plain English, voltage is held constant until the current falls to a predefined level.
Basic Absorption Charging Theory
As the battery charges, its resistance to a charge increases. When the voltage is held at a constant level, the increased resistance to a charge results in drop in current.
Ohms Law dictates what is going on here and can be seen in the graphic below.
What the Absorption Charge Process Adds to the Charging Process.
Excessive heat is an enemy to battery life. It can cause electrolyte to boil off and allow sulfation to set in.
By holding the voltage at a predetermined constant level, the amount of current is controlled. By monitoring that current until it falls to a defined level, the level of charge applied to the battery can easily be controlled.