According to one embodiment, a battery includes an external container, an electrode group, and a sealing plate. The electrode group includes a positive electrode and a negative electrode wound in a flat shape with an insulating layer interposed therebetween. Thicknesses TE of the positive and negative electrodes are each from 0.03 mm to 0.08 mm. A first direction is orthogonal to a winding axis direction of the electrode group. A second direction is parallel to the winding axis direction. The thicknesses TE of each electrode, a thickness TW of the electrode group in the third direction orthogonal to the first and second directions, and an innermost circumferential height HIC of the electrode group in the first direction satisfy 0.02≤(TE×TW)/HIC≤0.04.