NOVELTY - Apparatus comprises: a portable device (20) comprising a hydrogen reservoir (22) comprising a first hydrogen-storing material (23) with a charging pressure; at least one fuel cell (30) in fluid communication with the hydrogen reservoir; and a satellite refueling cartridge comprising a second hydrogen-storing material with a plateau pressure, where a pressure differential between the charging pressure of the first hydrogen-storing material and the plateau pressure facilitates transfer of the hydrogen from the satellite cartridge into the hydrogen reservoir.    USE - The apparatus is useful for storing and transferring hydrogen gas to be used as a fuel for fuel cells.    ADVANTAGE - The apparatus comprises a hydrogen-storing material that helps to provide a high volumetric energy density.    DETAILED DESCRIPTION - Apparatus comprises: a portable device (20) comprising a hydrogen reservoir (22) comprising a first hydrogen-storing material (23) with a charging pressure; at least one fuel cell (30) in fluid communication with the hydrogen reservoir; and a satellite refueling cartridge comprising a second hydrogen-storing material with a plateau pressure that is greater than the charging pressure of the first hydrogen storing material, where a pressure differential between the charging pressure of the first hydrogen-storing material and the plateau pressure of the second hydrogen-storing material facilitates transfer of the hydrogen from the satellite cartridge into the hydrogen reservoir to charge the first hydrogen-storing material, the satellite refueling cartridge is in fluid communication with the hydrogen reservoir by way of a detachable fluid coupling, and the transfer stops when the charging pressure of the first hydrogen-storing material becomes about equal to the plateau pressure of the second hydrogen-storing material or when an equilibrium state is reached between a pressure in the satellite cartridge and a pressure in the hydrogen reservoir.    DESCRIPTION OF DRAWING(S) - The figure shows a satellite cartridge containing a metal hydride and a fuel cell device comprising a hydrogen reservoir.    Portable device (20)    Hydrogen reservoir (22)    First hydrogen-storing material (23)    Fuel cell (30)    Refueling port (34)