NOVELTY - Glucose fuel cell has an anode (14) adapted to oxidize the glucose. A cathode (16) is adapted to reduce an oxidant and a membrane (18) is placed between the anode and the cathode and separating the anode from the cathode. The anode and the cathode is in the form of a flexible sheet (12) that is geometrically deformed into a shape receivable into the given constrained volume of implantation. The flexible sheet includes openings that accommodate fluid flow from one side of the flexible sheet to the other side of the flexible sheet.    USE - Glucose fuel cell for reception into given constrained volume of implantation in vertebrate in which the glucose fuel cell has access to fluid including glucose, for use in improvements in volumetric power densities of glucose fuel cells, for use in applications such as epilepsy and cardiac pacemakers in which flexible glucose fuel cell output trickles charge ultra-capacitor, which is then used for higher-power stimulation.    ADVANTAGE - The flexibility enables the construction of high-surface-area electrodes that fit within a small volume thus improving volumetric limits on oxidation or reduction current density at the electrode. Because the thin flexible sheet is readily deformed or rolled into a compact shape without breaking or harming the properties of the sheet, a high volumetric power density for the material is obtained which enables the operation of medical devices. To allow for variation in the glucose fuel cell output voltage, voltage regulation is incorporated into the circuitry, such that the chips are powered by a stable output voltage even if the output of the glucose fuel cell fluctuates over time. The power output provides a safety factor of three, allowing for the efficiency of the fuel cell to degrade over time while still safely powering the device.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method of making a glucose fuel cell for reception into a given constrained volume of implantation into a vertebrate in which the glucose fuel cell has access to fluid including glucose.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the glucose fuel cell that illustrates the structure of the fuel cell in surrounding body fluid.    Flexible sheet (12)    Anode (14)    Cathode (16)    Membrane (18)    Flexible mechanical substrate (20)