An integrated energy metering system having an energy meter including a voltage ADC for sensing voltage, a current ADC for sensing current, a microcontroller; a first memory device for storing program data for the energy meter; and a plurality of circuit blocks; a voltage monitor for monitoring a primary power supply; a power supply switch circuit for selectively applying one of the primary and auxiliary power supplies to the energy meter; and a system controller responsive to the voltage monitor for operating the switch circuit to apply the auxiliary power supply when the primary power supply voltage decreases below a predetermined level and gating the power to a first class of circuit blocks in the energy meter and applying power continuously to a second class of circuit blocks.