A fuel gauge for power supplies having a voltage pre-regulator; a main voltage regulator; a current sense resistor; an integrator with an op amp and capacitor, wherein the integrator receives power from the main voltage regulator, and receives a voltage proportional to current from the current sense resistor; a microprocessor with data storage and a hysteresis circuit, wherein the microprocessor operates in a low power state until activated by the resistor and the microprocessor converts the voltage proportional to current to a monotonic uni-polar representation of an aggregate number of electrons; a resistor disposed between the integrator and the microprocessor for activating the microprocessor from the low power state prior to saturation of the integrator with the voltage proportional to current; and a reset circuit disposed between the microprocessor and the integrator for resetting the monotonic uni-polar representation of an aggregate number of electrons to zero.