A battery cell includes a positive electrode, a negative electrode, and a separation film provided between the positive electrode and the negative electrode. A variation ratio of thickness of a battery cell before a pressurizing jig is disconnected and after the pressurizing jig is disconnected is equal to or less than 0.009, and the variation ratio of thickness of a battery cell is defied by a value generated by dividing a variation value of thickness that is a difference between the thickness of a battery cell after the pressurizing jig is disconnected and the thickness of a battery cell before the pressurizing jig is disconnected by the thickness of a battery cell before the pressurizing jig is disconnected.