Abstract: An energy conversion device includes batteries and a DC motor. A rotary member is driven by a hydraulic pump, which acts through pistons engaging a eccentric U-shaped rod to impart torque to the rotary member. Bevel gears transfer the torque to the rotary member, which can be connected to a DC generator or a battery charger. The pistons include hollow piston head and piston rods, which reduce the amount of hydraulic fluid that must be pumped. This energy conversion device may be employed in a vehicle, which may also employ a windmill as an auxiliary power source. Air is outlet from this windmill through hollow rotating windmill arms and through a hollow central shaft.