A riding mower includes a frame adapted to support a passenger and a cutting unit connected to the frame having at least one rotatably mounted blade. Interchangeable power unit support assemblies each support either an engine connected to a generator or a battery unit. One of the power unit support assemblies is releasably connected to the frame. A first electric motor is provided to rotate the blade and a second propels the mower. An output voltage generated by either the generator or the battery unit energizes the first and second electric motors.