Assembled Battery

Provided is an assembled battery in which a large number of flat batteries can be stacked easily. An assembled battery includes stacked multiple flat batteries A, B, and C in the shape of an N-sided polygon (N is an integer of 3 or more). Each of the multiple flat batteries A, B, and C in the shape of the N-sided polygon has a positive-electrode terminal and a negative-electrode terminal that extend in different directions having 360°/N in between, and the multiple flat batteries A, B, and C are electrically connected in series. The assembled battery also includes multiple N-sided polygonal separating films and disposed between each pair of adjacent ones of the stacked multiple flat batteries A, B, and C to insulate the flat batteries from one another.