An electric vehicle includes a transmission, motor, rechargeable energy storage system (RESS), auxiliary power unit (APU), and a controller. The APU has a pair of rings, at least one of which rotates with respect to the other. One ring is coaxial with and radially within the other. Ring rotation generates current in windings. A gear element is in driving connection with the rotatable ring. The APU includes an engine disposed radially within the inner ring, and a power takeoff mechanism coupled to the gear element. The controller energizes the APU to rotate a ring. A method includes positioning the APU in a vehicle body compartment, affixing an outer ring of windings to a compartment wall, and positioning a rotatable inner ring having permanent magnets radially within and coaxial with the outer ring. The engine is positioned radially within the inner ring. A power takeoff mechanism connects to the inner ring.