Abstract: An isolated dual power source system for isolating a first power source of a vehicle, connected to an engine starter, from a second power source of the vehicle which has an electrical circuit for distributing electrical power among the consumers, includes first and second switches for selectively connecting the first and second power sources to the electrical circuit, respectively. The system may include a controller that independently and operatively connects to the first and second switches to control operation thereof for selective and respective isolation from the electrical circuit. A third switch connecting the second power source to the starter may be used to selectively provide power thereto and bypass the first power source to start the engine.