Overcharging is charging beyond the time necessary to fully charge the battery or charging a battery at an excessive rate in amps. It results in corrosion of the positive grids and damage to the positive active material in the battery therefore reducing the battery’s ability to carry the starting current.
Overcharging is usually accompanied by heavy gassing (beware of the risk of explosion) that will accelerate the shedding of the active material from the positive plates.
Overcharging is also usually accompanied by high electrolyte temperatures resulting in rapid deterioration of the plates and separators. Overcharging may cause buckling of the plates leading to perforation of the separators and internal short circuits.