An assembly process for manufacture of zinc/air cells, typically zinc/air button cells. The cells have a cup shaped anode casing and cup shaped cathode casing, each having an open and closed end. The process comprises an assembly step wherein the two casings are pushed together, followed by a crimping step wherein the cell is punched through a die thereby crimping the cathode casing edge over the anode casing side wall with insulator seal therebetween. In each step, particularly in the crimping step, an anode punch having an annular protruding surface impacts the corner edge of the closed end of the anode casing while another punch is applied with an opposing force to the cathode casing. The process has particular utility for anode and cathode casings of small wall thickness, preferably between 2 and 5 mil (0.0508 and 0.127 mm).