NOVELTY - A hydrogen gas generating apparatus (100), comprises: a first chamber (102); a first mixture comprising a chemical hydride and a catalyst; a second chamber (104); a connector; a third chamber (106); a sealing element coupled to at least one of the second or third chamber; an outlet (214) fluidly coupled to the first chamber; and a resilient member (306) disposed within the third chamber and configured to control the flow of water into the first chamber via movement of the resilient member in response to hydrogen gas pressure within the apparatus.    USE - As hydrogen gas generating apparatus used in wearable power unit (claimed).    ADVANTAGE - The apparatus advantageously provides hydrogen gas to polymer electrolyte membrane fuel cell (PEMFC) array on an as-needed basis in a travel-convenient package. The apparatus produces a small amount of water vapor along with the hydrogen. The PEMFC array with the hydrogen fuel feed at the anode achieves efficient water removal from anode channels without intermittent anode gas ventilation, thus achieving high hydrogen fuel utilization efficiency. Excess water is conveniently evaporated from the PEMFC array surface.    DETAILED DESCRIPTION - A hydrogen gas generating apparatus (100), comprises: a first chamber (102); a first mixture comprising a chemical hydride and a catalyst disposed within the first chamber; a second chamber (104) coupled to the first chamber; a connector; a third chamber (106) coupled by the connector to the second chamber, and is fluidly coupled to the first chamber; a sealing element coupled to at least one of the second or third chamber; an outlet (214) fluidly coupled to the first chamber; and a resilient member (306) disposed within the third chamber and configured to control the flow of water into the first chamber via movement of the resilient member in response to hydrogen gas pressure within the apparatus. The first chamber is detachable from the second chamber; and comprises a first surface coupled to sidewalls, a rigid porous member disposed opposite the first surface and coupled to the sidewalls, a first filter coupled to the rigid porous member, and a first volume defined by the first surface, the sidewalls and the rigid porous member. The second chamber is detachable from the third chamber; and comprises a first surface coupled to sidewalls, where the outlet is coupled to the first surface, a second volume defined by the first surface and the sidewalls, and the first chamber is coupled within the second volume, and a second filter disposed between the outlet and the first chamber. The resilient member is an inflated bladder; and is a piston coupled to the third chamber by springs. The connector comprises a latch; and complimentary threads disposed in the second chamber and the third chamber that facilitate control of the coupling of the second chamber with the third chamber via a screwing motion. The sealing element comprises a gasket. The apparatus comprises a fuel cell coupled to the outlet. The third chamber comprises a third volume defined by a first surface and sidewalls; and is coupled by the connector to the second chamber, or coupled to the first chamber, and is configured to hold water. An INDEPENDENT CLAIM is included for a wearable power unit, comprising: a fuel cell; a belt attached to the fuel cell; and the hydrogen gas generating apparatus coupled to the fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows a hydrogen gas generating apparatus in varying stages.    Apparatus (100)    First chamber (102)    Second chamber (104)    Third chamber (106)    Tabs (116)    Porous hydrophobic first surface (200)    Rigid porous member (204)    Chemical hydride (208)    Catalyst (210)    First filter (212)    Outlet (214)    Second filter (222)    Resilient member (306)