Abstract: A sealing plug for a lead battery which prevents both the emergence of acid mist from the cell, and its harmful effects on the operation of the safety valve of the sealing plug, is configured to cause escaping cell gases to follow a path to the outside of the cell which first passes through a porous frit and which then proceeds through a pressure-release valve. To this end, a housing base is provided which includes a bottom portion for receiving the frit and for engaging a filler opening of the battery's lid. A premounted pressure-release valve including a compression spring and a sealing disk is retained between the housing base and a cap for engaging an outer flange of the housing base, for enclosing the resulting structure.