TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Parameters: The thermal conductivity of the hydrogen-containing material is directly or indirectly proportional to the releasable hydrogen content. The fuel level value corresponds to a pre-established minimum quantity of hydrogen gas that has been released from the hydrogen-containing material. The fuel level value corresponds to a quantity of releasable hydrogen remaining in the hydrogen-containing material; or the fuel level corresponds to a releasable fuel content of the hydrogen-containing material. Preferred Component: The hydrogen-containing material comprises aluminum hydride.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Device: The temperature sensor is disposed between the heat source and the fuel unit. The heat source is adjacent to a first portion of the fuel unit, and the temperature sensor is adjacent to a second portion of the fuel unit. The fuel unit comprises segregated quantities of the hydrogen-containing material. The fuel gauge comprises temperature sensors, each temperature sensor is disposed adjacent to a segregated quantity of the hydrogen-containing material. Fuel gauge comprises heat sources, each heat source is disposed adjacent to a segregated quantity of the hydrogen-containing material. The fuel gauge comprises a single heat source adjacent to each segregated quantity of the hydrogen-containing material and a single temperature sensor adjacent to each segregated quantity of the hydrogen-containing material. The hydrogen generator further comprises at least one of a visible display and an audible signal corresponding to one of hydrogen usage and releasable hydrogen remaining in the fuel unit. Hat source comprises an electric heater. The temperature sensor comprises a resistance temperature detector. The fuel unit comprises segregated quantities of the hydrogen-containing material, a separate heat source and a separate temperature sensor are disposed adjacent to each segregated quantity of the hydrogen-containing material, and a fuel output level is determined for individual segregated quantities of the hydrogen-containing material in a predetermined sequence. The temperature sensor is disposed between the heat source and the fuel unit. The temperature sensor is adjacent to a first portion of the fuel unit, and the temperature sensor is adjacent to a second portion of the fuel unit.