A small fuel cell (10) powers a portable electronic device (12) and contains a fuel reservoir (14) and a device (16) that measures the amount of liquid fuel (18) that is in the reservoir. The fuel cell operates on hydrogen that is obtained from a liquid hydrocarbon fuel, such as alcohol or other hydrocarbons. The liquid fuel is typically converted into hydrogen by a reforming process. The reservoir that is connected to the fuel cell has an indicia (19) that is readable by a human user of the portable electronic device, for measuring the amount of liquid hydrocarbon fuel that is present in the reservoir. Typically, the indicia consist of a sight glass, a capacitive element, a resistive element, a transparent portion of the reservoir, a float, or an acoustic transmitter coupled with an acoustic receiver.