An electrical system includes an engine, a motor-generator and a starter mechanism, and engine systems also include the engine. The electrical system includes a first energy storage device having a first voltage level and a second energy storage device having a second voltage level less than the first voltage level. The electrical system further includes a controller configured to control the motor-generator, the starter mechanism and first and second switching devices. Current from at least one of the first and second energy storage devices is delivered to the motor-generator when at least one of the first switching device is in a first closed state and the second switching device is in a second closed state such that the motor-generator transfers torque to the starter mechanism and the starter mechanism uses the torque to start the engine.