NOVELTY - A battery pack comprises a housing; fuel cell; temperature sensor and heating element both in thermally conductive communication with the fuel cell; secondary battery; and control mechanism responsive to a temperature sensed at the temperature sensor and is responsive for connecting the secondary battery to the heating element in the event of the sensed temperature being below a first predetermined level.    USE - For connection to a load (claimed) or electronic device (11).    ADVANTAGE - The battery pack prevents moisture from freezing in the fuel cell.    DETAILED DESCRIPTION - A battery pack (12) comprises a housing; fuel cell (16) within the housing; temperature sensor (13) in thermally conductive communication with the fuel cell; heating element (14) in thermally conductive communication with the fuel cell; secondary battery (17) within the housing; and control mechanism responsive to a temperature sensed at the temperature sensor. The secondary battery is selected to permit development of power to heat the heating element even when the temperature of the secondary battery is below the operating temperature of the fuel cell. The battery pack is disposed to be connectable to a load that can be turned on and off, and is disposed to be connectable to a fuel container (15). The fuel container when connected to the battery pack is disposed to deliver fuel to the fuel cell. The control mechanism is responsive to the condition of the load being connected or not, and to the condition of the load being turned on or not, and to the condition of a fuel container being connected to the battery pack or not, for connecting the secondary battery to the heating element in the event of the sensed temperature being below a first predetermined level, and the event of a load being connected and being turned on, and the event of a fuel container being connected to the battery pack. An INDEPENDENT CLAIM is also included for operating a battery pack cell adapted to be connectable to a load capable of being turned on and off, comprising:    (A) operating the fuel cell and charging a secondary battery;    (B) sensing a temperature at the fuel cell; and    (C) in the event of the sensed temperature dropping to a predetermined level, and in the event of a fuel container being installed to the battery pack, and in the event of the battery pack being connected to a load, and in the event of the load not being off, connecting the secondary battery to a heating element in thermally conductive communication with the fuel cell, thus warming the fuel cell.    DESCRIPTION OF DRAWING(S) - The figure shows a battery pack.    Electronic device (11)    Battery pack (12)    Temperature sensor (13)    Heating element (14)    Fuel container (15)    Fuel cell (16)    Secondary battery (17)