ELECTRIC POWER DEVICE, DISPLAY DEVICE, CHARGING RATE CALCULATION METHOD, PROGRAM, AND MEMORY MEDIUM

In an electric power device (10) and a charging rate calculation method according to the present invention, a control unit (30): calculates a sum total (FCC) of respective full charging capacities of a plurality of detachable/attachable batteries (16a-16d (16)); calculates a sum total (RC) of respective present charging capacities of the plurality of detachable/attachable batteries (16); and calculates an RSOC, which is an overall state of charge (SOC) of the plurality of detachable/attachable batteries (16), on the basis of the calculated sum total (FCC) of full charging capacities and the calculated sum total (RC) of present charging capacities.