An overcharged battery will boil the sulfuric acid and distilled water mix. The casing of the battery can become hot to the touch, and begin to melt or swell. Flammable hydrogen can build up inside the sealed cells of the battery, causing swelling of the casing under pressure and seepage through small vents.

What happens if you overcharge a battery?

Overcharging a battery causes excessive gassing — the electrolyte gets hot and both hydrogen and oxygen gas are generated. On older vented batteries, the electrolyte could cook away, leaving the plates exposed and ruining them. On sealed batteries, the buildup of gases could cause the battery to burst.

What are the symptoms of a battery that is being overcharged?

Signs of damage to an overcharged battery include swelling and cracks to the battery case caused by a buildup of gas and a loss of electrolyte fluid inside the battery. A battery will usually feel hot to touch after it has been overcharged.