NOVELTY - The casing comprises a cathode (6) cover (3) matching the anode (5) cup (2). The two components (2, 3) are united by a ring seal (4). A separator is also included. In novel design, within the cathode cover, close to the cathode and the separator, a non-perforated, open-pore: paper-, card- or plastic layer (7) is included. Its open pore system forms a venting disc, and is filled with paraffin oil (white oil). The cover, its components and the ring seal, form a pre-assembled unit, to be inserted into the anode cup.    USE - A button cell generating hydrogen and electricity.    ADVANTAGE - Paraffin oil filling of pores in the vent disc, prevents air from entering. Oxidation of electrochemically-active components of the cathode, with associated current flow, cannot occur. The paraffin oil is mobile within the pores, such that small, high-pressure hydrogen bubbles formed, are able to force their way out. When hydrogen generation ceases, the oil re-distributes itself in the pores, hence re-sealing against air entry. Electrodialitic migration from the cell is prevented, avoiding e.g. damage to high-value watches.    DETAILED DESCRIPTION - The cover is deep-drawn sheet metal with a cylindrical section and a base, which closes one end. The cover includes a central vent hole. The cylindrical vent disc rests on the inner surface of the cover and seals over the central vent hole. The anode cup has a cylindrical casing with an upper annular enlargement, into which the pre-assembled cover unit is inserted from above. A short circuit is used to cause reduction of oxides in the cathode region, without hydrogen generation, by equivalent zinc oxidation. This is achieved by bridging the anode to the cathode with a suitable resistance. The cell voltage is monitored and the short circuit is discontinued on reaching a constant value of about 0.5V. In this state the cell is ready for immediate hydrogen generation by connecting the cathode and anode, using a suitable resistance. The vent hole is sealed by an external sticker symbolizing freshness or readiness. AN INDEPENDENT CLAIM IS INCLUDED FOR the corresponding method of cell operation.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic cross section of the cell.    cover (3)    ring seal (4)    anode (5)    cathode (6)    open pore, oil-containing layer (7)