The invention relates to an apparatus (1) for converting chemical energy into electrical energy and/or electrical energy into chemical energy with a housing (2, 3, 3a), which is open towards at least one side (6) and in which a pressure chamber (4) is formed, and with at least one electrochemically active cell (5) for energy conversion, which extends from the open side (6) of the housing (2, 3, 3a) into the housing (2, 3, 3a), wherein the open side (6) is closed by a plate (7, 31), which holds and/or supplies power to the cell (5). A sealing element (8, 9) is arranged between the housing (2, 3, 3a) and the plate (7, 31), closes the open side (6) of the housing (2, 3, 3a) in a fluid-tight and/or gas-tight manner so as to form the pressure chamber (4) and is formed at least partially from an elastic material. At least one pocket (10) extending into the pressure chamber (4) is formed in the sealing element (8, 9), wherein the cell (5) is positioned in said pocket and the pocket wall (28) of said pocket is flexible as a result of the elastic material, with the result that the pocket wall (28) bears against the cell (5) in the event of an excess pressure in the pressure chamber (4).