Abstract: A housing for containing electrode assemblies and an electrolyte includes a cover 18 having a pair of long-side ends 18e. Peripheral thinned portions 11 are formed by cutting the inner face of a top plate 18a near the long-side ends 18e in parallel with the long-side ends 18e. A central thinned portion 15 is formed by cutting the central part of the outer face of the top plate 18a in parallel with the long-side ends 18e. This facilitates the rupture of a housing 1 due to an increase of the inner pressure, while ensuring the strength of the housing 1 to withstand external pressure.

Abstract: Disclosed is a battery 10 including: an electrode group including a positive electrode, a negative electrode, and a separator; an electrolyte; and a battery container accommodating the electrode group and the electrolyte. The battery container includes an accommodating portion 16 having an opening, and a lid sealing the opening of the accommodating portion 16. The battery container includes a liquid-retaining portion 16a retaining the electrolyte therein below the liquid surface of the electrolyte, and a gas-retaining portion 16b retaining gas therein above the liquid surface of the electrolyte. The liquid-retaining portion 16a of the side portion of the battery container is thinner than the gas-retaining portion 16b of the battery container. This suppresses scattering of fragments etc. in the event of rupture of a secondary battery due to an increase in the internal pressure. The safety of the secondary battery is thus increased.