NOVELTY - A fuel cell system (100) comprises housing(s); electrochemical cell(s) including electrolyte solution(s) disposed in housing, to receive reagent gas stream(s) and to vent exhaust gas stream(s); a humidity level control subsystem (110) disposed in housing, to maintain a humidity level at or near the equilibrium humidity level of electrolyte solution; a gas scrubbing subsystem (160) disposed in housing; and a reagent gas delivery subsystem disposed in housing, to deliver reagent gas stream to gas scrubbing subsystem. The humidity level control subsystem comprises humidity buffer solution.    USE - As a fuel cell system such as rechargeable fuel cell system and a metal hydride secondary battery (claimed), useful for power generation, transportation applications, portable power sources, home and commercial power generation, and large power generation.    ADVANTAGE - The fuel cell system has humidity level control subsystem that maintains humidity level of electrolyte solution; and gas scrubbing subsystem that removes the carbon dioxide from the reagent gas stream. The humidity buffer solution in humidity level control subsystem, provides a stable humidity level at or near the equilibrium humidity level of the electrolyte; and maintains water balance in the cell within a determined range. The scrubbing materials can adsorb carbon dioxide in low temperatures during the discharge process of the galvanic cell unit by either a chemical reaction, physical adsorption or both. The scrubbing materials can be regenerated within the scrubbing material layer by applying a thermal treatment to the resistance coil that is coupled to the scrubbing material during the charge period of the galvanic cell unit.    DETAILED DESCRIPTION - A fuel cell system comprises at least one housing having an interior surface defining a volume, and an air inlet and an air outlet; at least one electrochemical cell disposed within the housing and including at least one electrolyte solution, where the electrochemical cell is operable to receive at least one reagent gas stream, and to vent at least one exhaust gas stream; a humidity level control subsystem disposed within the housing and in vapor communication with the electrolyte solution, where the humidity level control subsystem is operable to maintain a humidity level at or near the equilibrium humidity level of the electrolyte solution; a gas scrubbing subsystem disposed within the housing, and which is upstream from the electrochemical cell and is in fluid communication with the reagent gas stream feeding the electrochemical cell; and a reagent gas delivery subsystem disposed within the housing, where the reagent gas delivery subsystem is in fluid communication with the gas scrubbing subsystem and is upstream from the gas scrubbing subsystem. The reagent gas delivery subsystem is operable to deliver the reagent gas stream to the gas scrubbing subsystem. The humidity level control subsystem comprises at least one humidity buffer solution. An INDEPENDENT CLAIM is included for operating the fuel cell system involving controlling a humidity level in an air space adjacent to an electrolyte; reducing a carbon dioxide content of a reagent gas stream prior to the reagent gas stream contacting the air space in an electrochemical cell having an electrode capable of consuming a portion of the reagent gas stream; and controlling access from a reagent gas stream source so that during a use mode in which the electrode is consuming the reagent gas stream portion, the air space is in fluid communication with the reagent gas stream source; and during non-use the air space is blocked from fluid communication with the reagent gas stream source.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of a fuel cell assembly having a gas scrubbing subsystem and a humidity level control sub-system.    Fuel cell system (100)    Humidity level control subsystem (110)    Fuel cell stack (152)    Shutters (140, 142, 144)    Gas scrubbing subsystem. (160)