Disclosed is an apparatus for preventing a battery from overcharging. In particular, the apparatus includes a battery module which has a plurality of battery cells and a battery controller that is connected to the battery module. The battery controller has a voltage sensor. A mounting frame is arranged a predetermined distance from the battery module, and is made of a conductor to which a ground is connected. The battery controller determines that overcharging to the battery module has occurred when the voltage sensor senses a low voltage due to the battery module coming in contact with the mounting frame because of swelling.