CELL PACK

[PROBLEM] In connecting a plurality of assembled batteries in parallel, to prevent a circulating current from exceeding an allowable current for the assembled battery. [SOLVING MEANS] A battery pack (100) has a plurality of assembled batteries (10-1 to 10-X) connected in parallel. Each of the assembled batteries has a plurality of cells (11) connected electrically. A circulating current in each of the assembled batteries is calculated from an open circuit voltage of the assembled battery that varies according to the number (N1 to Nx) of the cells connected in series, a value indicating a charge state of the assembled battery that varies according to the number (M1 to Mx) of the cells connected in parallel, and an internal resistance of the assembled battery. The number of the cells connected in parallel and the number of the cells connected in series in each of the assembled batteries are numbers determined under the condition that the circulating current should not exceed an allowable current value for the assembled battery.