Abstract: A mass plate electrode comprises a tablet of active material in a container of nickel gauze. The container consists of a cup and a lid which are joined by overlapping peripheral closure portions which are pressed into abutting attachment with each other to form an annular rim which is then bent over so as to embrace the side-wall portion of the cup.Prior to bending the rim over, the abutting closure portions of the cup and the lid are subjected to planishing or swaging to reduce the combined thickness of the two abutting closure portions by one half.