In the regenerative fuel cell, a positive chamber is separated from a negative chamber by a cation exchange membrane. The positive chamber comprises a positive electrode and a bromine-containing electrolyte. The negative chamber comprises a negative electrode and a sulfide-containing electrolyte. When the cell is in operation, the electrolytes are replenished using electrolyte from an electrolyte store (32, 34). In the method, the distribution of water between the two electrolytes is controlled by discharging the electrolyte(s), such that when the electrolytes are separated by a water permeable membrane (46), water will flow from the sulfide-containing electrolyte to the bromine-containing electrolyte by osmosis. The electrolytes are circulated through a container (43) which is divided by a water permeable membrane (46), under conditions wherein no current flows in the container between the two electrolytes.