Your regulator/rectifier is bad. Same thing hapoened on my old fat boy. Blew my headlight bulb and smelled acid. Replace the battery and regulator you should be good to go. The regulator is built to charge the baterry and the excess is dissipated to ground. When the circuit goes bad it can stick closed allowing continuous charge. Bang goes the battery.
The regulator/ rectifier is suppose to shunt excess electricity as heat, when it cannot it backs up and will blow the battery, melt wires and take out the stator also
