. . . "Here, the MPU 15, for example, in a memory portion 17, stores in advance information on correlation (refer to FIG. 3) between a voltage and a remaining capacity (here, a remaining capacity is specified by WH (Watt hour), according to type of the battery portion 10 currently used, for example, type such as a lithium ion battery or type, or a nickel hydrogen battery." . . . .