Method of operating a fuel cell/battery passive hybrid power supply

The method of operating a passive hybrid power supply in, or near, zero connected load conditions comprises the steps of : - supplying a stream of substantially pure hydrogen to the anode of said fuel cell; - supplying an stream of substantially pure oxygen to the cathode of said fuel cell; - monitoring an electric current supplied by the storage battery; - monitoring an output voltage shared by the fuel cell and the battery; - evaluating a state of charge (SOC) of the battery based on said electric current and said output voltage; - monitoring a hydrogen pressure in the fuel cell; - monitoring an oxygen pressure in the fuel cell; - limiting the stream of hydrogen and the stream of oxygen and actuating the hydrogen and oxygen recirculating pumps in such a way as to bring and maintain the hydrogen and oxygen pressures below .7 bar absolute while maintaining said hydrogen pressure between 70 and 130 % of said oxygen pressure, in such a way as to ensure that the output voltage is maintained at a level corresponding to less than .90 volts/cell and does not exceed the maximum voltage limit of the battery.