PURPOSE: To make it possible to supply adequate battery voltage to an electric appliance by conducting internal wiring which connects in series or in parallel the multiple battery units in a battery pack in accordance with voltage required to the electric appliance to its appliance connectors.

CONSTITUTION: Appliance side connectors 14, 15 having internal wiring for connecting multiple battery units 3a, 3b in series or in parallel are arranged in electric appliances 12, 13 which use battery voltage supplied by connecting in series or in parallel the multiple battery units 3a, 3b in a battery pack 1. By connecting the appliance side connectors 14, 15 to a battery side connector 9, the multiple battery units 3a, 3b are connected in series or in parallel, and then connected to either one of corresponding appliances 12, 13. Battery voltage is supplied to the appliances 12, 13 in accordance with their necessary voltage values without the switching operation of battery voltage with switches.