The only way to "overcharge" a battery is to place to high a back voltage on it. This can happen if the regulator is defective. Check the system voltage with the engine idling and accessories off. It should be 13.5 - 14.5 volts.

Rev the engine and it should hold in this range. If it goes over about 14.5 the regulator is probably defective.

A fully charged battery should measure about 12.6 volts at 80 degrees F. It's the higher system voltage that charges the battery. A battery charger works the same way. If an overvoltage is applied for too long the electrolyte can "boil" out of the battery.

Duke