A battery (10) comprises a safety vent assembly (100). The safety vent assembly (100) comprises a sealing member (104) and an urging member (106) to urge the sealing member (104) against a venting aperture (105) on a battery reaction chamber to seal the battery reaction chamber when pressure inside the battery reaction chamber is below a venting threshold pressure under normal operation conditions, wherein the sealing member (104) is operable to provide a venting path to vent gas from the battery chamber when pressure inside the battery chamber reaches the venting threshold pressure which is sufficient to overcome the urging force of the sealing member (104), and wherein the urging member (106) is to permanently deform on reaching a venting threshold temperature such that gas venting from the battery chamber will occur at a pressure below the venting threshold pressure.