A battery exterior body which can be easily manufactured without additional process by heat-sealing internal layers of battery exterior materials, and has a high degree of safety with respect to gas generated in the inside of the exterior body, a method of manufacturing the battery exterior body, and a lithium secondary battery are provided. The battery exterior body is a battery exterior body 2 which is formed by heat-sealing internal layers 8 of battery exterior materials 4 formed by laminating an external layer 11 including a heat-resistant resin film, a metal foil layer 10, and the internal layer 8 in this order, and has a sealing strength between the heat-sealed internal layers 8 of 20 N/15 mm of width to 50 N/15 mm of width.