TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Device: The fuel cell comprises a phosphoric acid fuel cell, alkaline fuel cell, a proton exchange membrane fuel cell, or a solid oxide fuel cell. The fuel cell comprises bipolar plate(s) that comprises the anode of one fuel cell in the stack and the cathode of an adjacent fuel cell in the stack; a fuel recycle conduit that connects the water vessel to the fuel conduit; a housing comprising a cylindrical wall; and a downhole electrical device which is electrically connected to the fuel cell.Preferred Component: The reaction zone comprises, as its only openings for fluid flow:(a) aperture(s) connected to the fuel conduit for admitting fuel into the reaction zone;(b) aperture(s) connected to the oxidant conduit for admitting oxidant into the reaction zone; and(c) capillary flow path(s) that connects the reaction zone to the water vessel.The bipolar plate (34) comprises two planar surfaces. The fuel vessel comprises a source of hydrogen gas. The oxidant vessel comprises oxygen gas.Preferred Condition: The fuel, oxidant or water does not dynamically flow in a closed loop through the reaction zone. The pressure in the reaction zone is 40-400 psig. The pressure of the oxygen gas in the oxidant vessel is at least 1000, preferably 5000 psig. The fuel cell is electrically connected to a battery to form a hybrid power source. It is operated at least 100, preferably 120 degrees C. The fuel cell can operate in environments with temperatures of 0-1000 degrees C.Preferred Component: The fuel cell has a power output of at least 1 watt for a period of more than one day.    TECHNOLOGY FOCUS - POLYMERS - Preferred Material: The electrolyte comprises a polymer.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The water vessel comprises a metal hydride material that is capable of releasing hydrogen gas when in contact with the water.    TECHNOLOGY FOCUS - CERAMICS AND GLASS - Preferred Material: The electrolyte comprises a solid ceramic.