NOVELTY - Hydrogen generator comprises a replaceable fuel unit containing a hydrogen-containing material that can release hydrogen gas when heated; and a fuel gauge comprising a heat source adjacent to the fuel unit, a temperature sensor adjacent to the fuel unit for measuring a temperature, and a controller for determining a fuel level value based on the measured temperature at a pre-established time and a predetermined relationship between the measured temperature and a releasable hydrogen content of the hydrogen-containing material at the pre-established time.    USE - The hydrogen generator or method is useful for fuel gauging (claimed).    ADVANTAGE - The hydrogen generator makes use of some of the components required to produce hydrogen gas for fuel gauging, thus minimizing the number of components required solely for fuel gauging, avoiding unnecessary complexity, and minimizing the manufacturing cost of both the hydrogen generator and the fuel units used in it.    DETAILED DESCRIPTION - Hydrogen generator comprises a replaceable fuel unit containing a hydrogen-containing material that can release hydrogen gas when heated and whose thermal conductivity is related to a quantity of releasable hydrogen contained in it; and a fuel gauge comprising a heat source adjacent to the fuel unit, a temperature sensor adjacent to the fuel unit for measuring a temperature, and a controller for determining a fuel level value based on the measured temperature at a pre-established time and a predetermined relationship between the measured temperature and a releasable hydrogen content of the hydrogen-containing material at the pre-established time. An INDEPENDENT CLAIM is included for a method of fuel gauging which involves: (a) providing a hydrogen generator comprising a housing, a fuel unit containing a hydrogen-containing material disposed in the housing, a heat source adjacent to the fuel unit, and a temperature sensor adjacent to the fuel unit; (b) activating the heat source; (c) measuring a temperature with the temperature sensor at a pre-established time after activating the heat source; (d) processing the measured temperature to determine a fuel level value based on the measured temperature; and (e) generating an output signal corresponding to the fuel level value.