Described herein is, for example, a battery or capacitor over voltage (overcharge) and under-voltage protection circuit, that, for example, is adapted to not draw current from the battery or capacitor to be charged unless charge energy is detected and to not charge an energy storage device when an over-charge condition is sensed. The protection circuit may, for example, not be turned on unless an over voltage condition is present. Incoming energy to the system can be shunted to ground via a shunt load of various types including resistive loads and active components such as a zener diode. In some embodiments, no switching of the inbound power is required. Within limits, no regulation of inbound power is needed. When inbound power is sufficient to charge the battery or capacitor, regulation can occur via the applied shunt regulator if overcharge voltage conditions exist. Either type of charge source, voltage or current, can be used to provide charge energy. Combining said battery or capacitor over voltage (overcharge) and under-voltage protection circuit with electronic loads, such as wireless sensors, may lead to autonomously-powered wireless sensor systems.