Provided is a method of manufacturing a battery having an electrode module including: a positive plate having a cathode collector portion formed by attaching a lead member to a cathode substrate made of a foamed metal plate; and a cathode collector plate welded to the cathode collector portion. The method includes: a pre-welding positive plate forming process of forming a pre-welding positive plate, which is the positive plate before welding, such that the pre-welding positive plate has a projection projecting from a pre-welding cathode collector portion, which is the cathode collector portion before welding; and a welding process of melting a pre-welding cathode collector plate to weld it to the projection. In the pre-welding positive plate forming process, the projection is formed into such a shape that the condition that S≦1.3W is satisfied, where W and S represent the width and the circumferential length of the projection, respectively.