A battery packet (50) comprises a battery case (51) formed by processing a battery case forming laminated sheet (10), a battery 50a contained in the battery case (51), and tabs (59, 60) extending outside from the battery case (51). The battery case forming laminated sheet (10) is formed by laminating a first base film layer (1a), i.e., an outermost layer, a metal foil layer (2), and a heat-adhesive resin layer (3) in that order. The first base film layer (1a) is a biaxially oriented polyethylene terephthalate resin film or a biaxially oriented nylon resin film. The metal foil layer (2) is an aluminum or copper foil. The heat-adhesive resin layer (3) is formed of a polyolefin resin, more preferably, of an acid-denatured polyolefin resin.