NOVELTY - A regenerative fuel cell apparatus comprises an electrolyzer unit having a cathode, an anode and a gas bypass conduit; and a fuel cell unit having a fuel cell anode, a fuel cell cathode and coolant channel(s). It includes connection(s) between the electrolyzer unit and the fuel cell unit.    USE - As a regenerative fuel cell apparatus.    ADVANTAGE - The inventive apparatus enables improved fuel cell performance, including rapid switchover between the fuel cell and electrolyzer modes, instantaneous full power operation, higher power density, less peripherals and high system efficiency.    DETAILED DESCRIPTION - A regenerative fuel cell apparatus comprises an electrolyzer unit (30); and a fuel cell unit (20). The electrolyzer unit comprises a cathode including first (60) and second electrolyzer cathode ports; an anode including first (63) and second electrolyzer anode ports; and a gas bypass conduit including first (62) and second gas bypass ports. The fuel cell unit comprises a fuel cell anode including first and second fuel cell anode ports; a fuel cell cathode including first (50) and second fuel cell cathode ports; and coolant channel(s) including first (53) and second coolant ports. The regenerative fuel cell apparatus/system includes a connection between the second electrolyzer cathode port and the second fuel cell anode port to provide a continuous passage between the first electrolyzer cathode port and the first fuel cell anode port for hydrogen; a connection between the second electrolyzer anode port and the second coolant port to provide a continuous passage between the first electrolyzer anode port and the first coolant port; and/or a connection between the second gas bypass port and the second fuel cell cathode port to provide a continuous passage between the first gas bypass port and the first fuel cell cathode port.    An INDEPENDENT CLAIM is also included for a method of operating the regenerative fuel cell apparatus, comprising in a fuel cell mode operation, supplying hydrogen and an oxidant to the fuel cell to generate electricity, withdrawing water from the fuel cell and passing a coolant through the fuel cell, where the method includes passing the fuel gas, the oxidant and/or the water through the electrolyzer unit; and in an electrolyzer mode of operation, supplying water to the electrolyzer and electric current to electrolyzer water to generate oxygen and hydrogen and withdrawing oxygen, hydrogen and residual water from the electrolyzer, where the method includes passing water, oxygen and/or hydrogen through the fuel cell unit.    DESCRIPTION OF DRAWING(S) - The figure is an exploded perspective view of a regenerative fuel cell system.    Fuel cell unit (20)    Fuel cell anode bipolar plate (21)    Fuel cell cathode bipolar plate (22)    Fuel cell membrane exchange assembly (23)    Electrolyzer unit (30)    Electrolyzer anode bipolar plate (31)    Electrolyzer Cathode bipolar plate (32)    Electrolyzer membrane exchange assembly (33)    Common separator plate (40)    First fuel cell cathode port (50)    First coolant port (53)    First electrolyzer cathode port (60)    First gas bypass port (62)    First electrolyzer anode port (63)    End plates (70, 80)