Abstract: A disc formed of a resilient plastic exhibiting a low creep characteristic and having a pressure vent is used to close the mouth of a tubular cell envelope of a primary cell. An elongated terminal is inserted through the disc and into the cell interior. The pressure vent is in the disc at a location between the terminal and the edge of the disc. The vent comprises a recess having a frangible diaphragm with at least one groove. At a predetermined pressure the diaphragm breaks at the groove, releasing pressure.

Abstract: The mouth of a tubular cell envelope is closed by compressing into it an end cap formed of a resilient plastic exhibiting a low creep characteristic. An elongate terminal is inserted through the end cap and into the cell interior, and a vent passage is formed in the cap at a location between the electrode and the cap edge. In one embodiment a plug is placed in the passageway before assembly of the end cap into the envelope such that the radial compression of the end cap by the surrounding envelope clenches the plug more tightly in the passageway. In a preferred embodiment, the plug is formed with a hollow core and the outer end of the passageway is counterbored or chamfered to allow the plug to be blown clear of the passageway by undesirably high pressure generated within the cell.