Abstract: A lithium-ion or polymer-ion battery or generally a battery with electrolyte that is incompatible with water. The battery has a battery cell and a gas-tight casing around the battery cell. A vent is arranged in the casing and configured to allow exit of gases from the battery cell. The vent contains a body with a circumferential wall defining an external surface and a space within the body. The external surface provides a sealing surface configured for hermetic sealing the vent to the casing. The vent further contains a gas separation element for passing through gases from the battery cell and for substantially inhibiting electrolyte of the battery cell from passing through, configured to divide a given portion of the space defined by the circumferential wall into a first chamber and a second chamber.