A microcontroller-based electronic device and its operating methods are operable to learn a critical voltage value for a microprocessor control unit residing in the microcontroller-based electronic device. The microprocessor control unit receives power from a battery. An exemplary embodiment detects an operating voltage provided to the microprocessor control unit by a supplemental power reservoir after removal of the battery, stores information corresponding to a value of the operating voltage in a nonvolatile memory, repeats the detecting and the saving information as the operating voltage decays in response to a discharge of the supplemental power reservoir, and determines the actual minimum operating voltage for the microprocessor control unit based on a last one of the stored information corresponding to the value of the operating voltage. A learned critical voltage value is based upon the defined actual minimum operating voltage.