NOVELTY - Biofuel cell device (I) comprises: a fuel manifold; at least one cavity in the manifold defining a fuel reservoir (807); an inlet for flow of fuel fluid into the manifold to fill the reservoir; an anode-cathode assembly (815); a housing for housing the manifold and the anode-cathode assembly; a controller for controlling the output of electrical current from the biofuel cell device; a passive fluid management system for controlling a moisture condition inside the housing; and a venting system for venting carbon dioxide gas from the fuel reservoir.    USE - (I) is useful for: generating electrical current; and supplying electrical power to a load (all claimed).    ADVANTAGE - (I) can be stored for short and/or long term durations.    DETAILED DESCRIPTION - Biofuel cell device comprises: a fuel manifold; at least one cavity in the manifold defining a fuel reservoir; an inlet for flow of fuel fluid into the manifold to fill the reservoir; an anode-cathode assembly comprising at least one anode positioned for contact with fuel fluid in the fuel reservoir and at least one biocathode positioned for flow of an oxidant to a biocathode enzyme; a housing for housing the manifold and the anode-cathode assembly; a controller for controlling the output of electrical current from the biofuel cell device; a passive fluid management system for controlling a moisture condition inside the housing; and a venting system for venting carbon dioxide gas from the fuel reservoir. INDEPENDENT CLAIMS are included for:    (1) a biofuel cell device comprising: at least one fuel cell; a controller for controlling an electrical output of the fuel cell according to a defined operating mode; and a metal-oxide-semiconductor field-effect transistor (MOSFET) switching circuit situated between the fuel cell and the load, where the switching circuit being responsive to the controller for alternately connecting the electrical output of the fuel cell to the load and disconnecting the electrical output of the fuel cell from the load according to the operating mode;    (2) a biofuel cell device comprising: at least one fuel cell; a power switch for manually selecting either an active state or an inactive state of the biofuel cell device, where the power switch containing a magnet; and a controller for controlling an electrical output of the fuel cell according to a defined operating mode when the biofuel cell device is in the active state, where the controller comprises a Hall Effect sensor responsive to the magnet contained in the power switch for setting the biofuel cell device to the selected active state or selected inactive state;    (3) a biofuel cell comprising: an alkaline fuel fluid; an oxidant; an anode capable of oxidizing the fuel fluid and releasing electrons; a biocathode comprising a cathode enzyme capable of reacting with the oxidant to produce water; and an anion exchange membrane;    (4) a biofuel coin cell device for generating electrical current, comprising: at least one reservoir containing a fuel fluid; at least one anode-cathode assembly comprising at least one anode positioned for contact with fuel fluid in the reservoir and at least one biocathode positioned for flow of air to a biocathode enzyme; an external biocathode terminal electrically connected to the at least one anode-cathode assembly; and an external anode terminal electrically connected to the at least one anode-cathode assembly; and    (5) a biocathode comprising: an electron conductor; a cathode enzyme capable of gaining electrons from the electron conductor and reacting with an oxidant to produce water; a precious metal catalyst or a combination of metal complexes, where each metal complex in the combination has a different reduction potential; and an enzyme immobilization material capable of immobilizing and stabilizing the enzyme; and the immobilization material being permeable to the oxidant.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective of the coin cell device.    Reservoir body (805)    Reservoir (807)    Anode-cathode assembly (815)    Reservoir end cap (821)    External cathode terminal. (825)