PURPOSE: To improve resistance to liquid leakage by forming a sealing agent layer of a mixture of polystyrene-polyisoprene block copolymer and polyisobutylene in a sealing part between a gasket and a sealing plate and a sealing part between the gasket and a battery case.

CONSTITUTION: A solution mixture containing polystyrene-polyisoprene block copolymer and polyisobutylene and diluted with toluene is previously applied to the inner walls of a battery case 5 and dried. In the same way in a sealing part in a sealing plate 1 side, the inner walls of a gasket 6 is treated. The copolymer to be used is a block copolymer comprised of polystyrene molecules and hydrogenated polyisoprene molecules. A battery is fabricated by combining with the sealing plate 1. As a result, resistance to liquid leakage is improved and at the same time the sealing agent is prevented from being pushed out.