US Patent 7825615 Intelligent motorized appliances with multiple power sources

A motorized portable appliance which monitors, and automatically selects, one of multiple power sources. The motorized portable appliance includes an electric motor, a secondary battery and at least one other source of electrical power, and an automatic control to switch between the secondary battery and the other source of electrical power, which may be mains electrical power, an external secondary battery, an on-board secondary battery, an automotive battery, a solar photovoltaic array, or a primary battery. Power conditioning circuitry converts power from the various power sources to a form compatible with the electric motor and recovers remaining power from depleted primary batteries.