A battery pack has a communicator storing various communication protocols. When new hardware is connected thereto, the battery pack sequentially transmits a respective communication request signal to request communication with the hardware using a stored communication protocol, and establishes communication. The battery pack transmits the communication request signal using a standard such as a compatibility priority among communication protocols, a frequency priority for communication protocols used according to a history record, a communication speed priority for communication protocols, and so on, thereby achieving quick establishment of communication.