NOVELTY - A filling system (10) comprises a first fuel supply (12) having at least one first valve connector (9) arranged to supply fuel to first fuel chamber (13) having at least a second valve connector (20). The first and second valve connectors are connectable so that the fuel supply refills the fuel chamber.    USE - For refilling fuel cartridges.    ADVANTAGE - Electronic devices having large fuel cartridges, e.g. laptop computer, can be used to re-fill smaller fuel cartridges, and small cartridges can be emptied into a larger cartridge for transportation, recycling or other environmental reasons. This arrangement obviates the need for carrying a separate container especially for holding spare fuel, since the fuel cartridge can be used directly with a fuel cell or as a spare fuel supply. The second fuel cartridge is refilled and not discarded. The level of the fuel in the receiving fuel cartridge is monitored to control the amount of fuel transferred to the fuel chamber. Once the chamber has been refilled to the desired level, the fuel supply and the fuel chamber are disconnected. The connection points are then sealed to prevent leakage. The sealing may take place manually or automatically. The connection points are retracted into the cartridge or electronic device to prevent damage to the connectors. The entire system is arranged to be operated manually or automatically, and the status of the system can be indicated on a display mounted to the adapter, electric device or the cartridge.    DETAILED DESCRIPTION - A filling system (10) comprises a first fuel supply (12) having at least one first valve connector (9) arranged to supply fuel to first fuel chamber (13) having at least a second valve connector (20). The first and second valve connectors are connectable so that the fuel supply refills the fuel chamber. When the valve connectors are not connected to each other the first valve provides a seal for the fuel supply and the second valve connector provides a seal for the fuel chamber. The fuel chamber comprises fuel cartridge supplying fuel to fuel cell. The fuel cartridge is located internal to the electronic device. One of the fuel supplies comprises a system for monitoring the amount of fuel contained in it and an adapter is in communication with the fuel monitoring system.    An INDEPENDENT CLAIM is included for an adapter for connecting a first fuel supply to the second fuel supply.    DESCRIPTION OF DRAWING(S) - The figure shows a perspective view of a filling system.    filling system (10)    first fuel supply (12)    first valve connector (9)    first fuel chamber (13)    second valve connector. (20)