NOVELTY - The method comprises counting electrons flowing through a battery to create an electron count, determining whether the electron count reaches a predetermined number, activating a storage device to add the electron count to a total count after the electron count reaches the predetermined number, resetting the electron count after the electron count reaches the predetermined number, and determining a capacity of the battery from the total count. The step of counting the electrons comprises measuring a current, converting the measured current into a voltage.    USE - The method is useful for measuring electron flow to determine remaining capacity of a power supply such as a lithium primary battery, a lithium ion battery, a lead-acid battery, a fuel cell, a solar panel system, or other power supply.    ADVANTAGE - The method accurately measures and tracks electron flow using an apparatus that is portably usable in many environments, easy to undertake and inexpensive to operate, and can be implemented on a wide variety of power supplies for remote and close proximity monitoring of electron usage by a customer, a user and an administrator simultaneously in real time.    DETAILED DESCRIPTION - The method comprises counting electrons flowing through a battery to create an electron count, determining whether the electron count reaches a predetermined number, activating a storage device to add the electron count to a total count after the electron count reaches the predetermined number, resetting the electron count after the electron count reaches the predetermined number, and determining a capacity of the battery from the total count. The step of counting the electrons comprises measuring a current, converting the measured current into a voltage, and integrating the voltage to obtain the electron count. The current is measured through a resistor (14) coupled in series with the battery. The capacity is determined by comparing the total count to a calibration value. The calibration value is based, in part, on a standard unit of capacity measurement for the battery. The method further comprises measuring an ambient temperature of the battery, adjusting the calibration value based, in part, on the ambient temperature, communicating the capacity, through a network, to a remote monitor, and repeating the step of counting electrons, the step of activating the storage device, and the step of resetting the electron count. INDEPENDENT CLAIMS are included for:    (1) a method for determining power supply usage; and    (2) an apparatus for measuring electron flow to determine remaining capacity of a power supply.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a fuel gauge used for measuring electron flow.    Voltage pre-regulator (10)    Main voltage regulator (12)    Current sense resistor (14)    Integrator (16)    Operational amplifier (18)    Capacitor. (20)