Plug assembly

The invention relates to a stopper assembly for gas-tight closure of a cell opening (2) of an accumulator. In order to provide a stopper assembly that prevents leakage of acid even when an accumulator is tilted or rotated, while simultaneously allowing sufficient degassing and is furthermore economically producible, easy to assemble, and adaptable to different accumulator designs, the present invention proposes a stopper assembly for gas-tight closure of a cell opening (2) of an accumulator, formed from a closure stopper (4) that can be sealingly inserted into the cell opening (2), wherein the cell interior (3) for acid separation is in fluid communication via an opening (10) provided with a two-way sealing membrane (12) of the lateral surface (11) of the closure stopper (4) with a cavity (5) formed between upper and lower covers (6, 7) of the housing cover (17).