Abstract: A liquid retaining pressure relief valve for electrochemical battery cells is provided including a pressure regulator and a membrane vent that are mounted to the top and bottom ends of a threaded valve housing or plug. The valve housing or plug screws into the cell cover from the outside of the cell such that the membrane vent is internal to the cell. The membrane vent includes a thin gas permeable liquid repellant membrane that is molded into the body of the vent. The membrane is preferably composed of an expanded polytetraflouroethylene (ePTFE) polymer.