A battery comprises at least two unit cells. Each of the at least two unit cells is provided with an outer sheath film composed of polymer-metal composite material, a positive-electrode current collector, a negative-electrode current collector, a separator disposed between the positive-electrode current collector and the negative-electrode current collector, one positive electrode tab to which the positive-electrode current collector is connected and protruding from a first sealed portion of the outer sheath film, one negative electrode tab to which the negative-electrode current collector is connected and protruding from a second sealed portion of the outer sheath film, a first polymer layer disposed between the positive electrode tab and the outer sheath film, and a second polymer layer disposed between the negative electrode tab and the outer sheath film.