A thermostat includes a plurality of HVAC (heating, ventilation, and air conditioning) wire connectors for receiving a plurality of HVAC control wires corresponding to an HVAC system. The thermostat also includes a thermostat processing and control circuit configured to at least partially control the operation of the HVAC system and a powering circuit coupled to the HVAC wire connectors and configured to provide an electrical load power to the thermostat processing and control circuit. The powering circuit has a power extraction circuit configured to extract electrical power from one or more of the plurality of received HVAC control wires up to a first level of electrical power, a rechargeable battery, and a power control circuit. The power control circuit is configured to provide the electrical load power using power from the power extraction circuit and the rechargeable battery.