A battery pack includes: a secondary battery; a positive electrode terminal for connecting a positive electrode of the secondary battery to an external electric device; a negative electrode terminal for connecting a negative electrode of the secondary battery to the electric device; a communicator for communicating with the electric device; a communication terminal adapted to be used in connecting the communicator to the electric device to send a signal for the communication; and an electric power receiving terminal for receiving an electric power from the electric device to operate the communicator, wherein the communicator is operated by the electric power received by the electric power receiving terminal.