A filling device (1) for decentralized filling of a gas cylinder (10) with a medical gas in a medical facility (100), comprises a connection unit (2) for connection to a wall outlet (134) of a centralized gas supply system (130) of the medical facility (100). A receiving unit (3) for receiving the gas cylinder (10) to be filled, and a filling unit (4) for filling the received gascylinder (10) with the gas supplied by the wall outlet (134) and a corresponding system and method. The filling device may have a communication arrangement for receiving an ID associated with the cylinder. The device may be portable.