The battery pack is provided with communication lines that connect with attached electrical equipment, a temperature-sensing element that connects with a communication line, a switching device that connects with the temperature-sensing element, and a control section to control the switching device. The control section puts the switching device in the open state when the communication lines are being used and puts the switching device in the closed state when the communication lines are not being used to output temperature-sensing element voltage to the electrical equipment-side via the communication lines.