A battery pack having a housing and a secondary battery inside the housing, and including a communicator that receives an instruction related to the secondary battery from an external communication terminal device via short-distance wireless communication and a controller that executes an operation in accordance with the instruction by using a status of the secondary battery. The external communication terminal device, by transmitting to the battery pack the instruction, which is related to the status of the secondary battery, acquires a response that is in accordance with the status of the secondary battery from the battery pack, thereby facilitating checking of secondary battery state.