NOVELTY - The generator comprises a holder provided with a cavity. A packaged fuel unit (10) is replaceably arranged within the cavity and comprises: a set of segregated quantities of fuel, each comprising a reactant that undergoes a thermal decomposition reaction to produce hydrogen gas when heated to a minimum initiation temperature; and a package comprising a container (12) in which the segregated quantities of fuel is disposed and is covered by a lid (14). A heating system includes a set of heaters that are in thermal communication with one of the thermal conductor sections (18).    USE - The hydrogen generator is useful in a fuel cell battery of a fuel cell system to produce the hydrogen gas, where the fuel cell is proton exchange membrane fuel cell, alkaline fuel cell, phosphoric-acid fuel cell, solid oxide fuel cell and molten carbonate fuel cell, and the fuel cell battery is used as a power source in a portable electronic device.    ADVANTAGE - The packaged fuel unit contains a maximum quantity of reactant to produce a maximum quantity of hydrogen gas, has a simple design and is easy and inexpensive to manufacture, reliably contains the contents before and after use, provides excellent heat transfer to the reactant; and has a package that facilitates selective heating of individual segregated quantities of reactant to provide hydrogen on an as-needed basis. The hydrogen generator can produce the hydrogen gas in a safe and economical manner. The fuel units can be easily and safely replaced. The holder contains a maximum number of expensive and reusable components. The heating system can be controlled to heat the reactant and provide hydrogen on an as-needed basis.    DETAILED DESCRIPTION - The hydrogen generator comprises a holder provided with a cavity. A packaged fuel unit (10) is replaceably arranged within the cavity and comprises: a set of segregated quantities of fuel, each comprising a reactant that undergoes a thermal decomposition reaction to produce hydrogen gas when heated to a minimum initiation temperature; and a package comprising a container (12) in which the segregated quantities of fuel is disposed, where the container is made of a material with a poor thermal conductivity of less than 5 W/mK and is covered by a lid (14) that is made of material having a poor thermal conductivity of less than 5 W/mK. The lid includes a set of apertures that are covered by thermal conductor sections (18), where each thermal conductor section is in contact with at least one of the segregated quantities of fuel. The fuel unit comprises a hydrogen outlet through which hydrogen gas is discharged. A heating system includes a set of heaters, where each of the heaters is in thermal communication with at least one of the thermal conductor sections. The container comprises a set of compartments, each containing at least one of the segregated quantities of fuel. The apertures of the lid are covered by one of the thermal conductor sections, where each of the thermal conductor sections is bonded to the lid with a discontinuous bond and with a continuous bond. The lid is bonded with adhesive bonds, ultrasonic bonds, and heat bonds. The container is made of flexible glass. A thermal insulation (28) is arranged between the adjacent segregated quantities of fuel, where the thermal insulation comprises a paper through which the hydrogen gas passes. The reactant is sufficiently exothermic for each segregated quantity of fuel to undergo a self-sustaining hydrogen generating reaction after being heated to at least the minimum initiation temperature. Each of the segregated quantity of fuels is in contact with an ignition material that undergoes the self-sustaining reaction after being heated to an initiate reaction of the ignition material such that the heat is provided to sustain the hydrogen generating reaction in the segregated quantity of fuel until the reactant is consumed.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic exploded perspective view of a hydrogen generator.    Fuel unit (10)    Container (12)    Lid (14)    Thermal conductor sections (18)    Thermal insulation. (28)