An auxiliary power system for a motor vehicle includes a power generator that generates electricity to charge one or more auxiliary power system batteries. The motor vehicle includes an engine and drive train that distributes power from the engine to the drive wheels. The drive train can include a transmission, a drive shaft and a differential that connects the engine to the drive wheels. The power generator can be connected to the drive train (e.g., the transmission, the drive shaft or the differential) to draw power to generate electricity as well as to apply braking loads on the drive wheels to increase the ability to stop the motor vehicle.