US Patent 9630514 System and method for vehicle power management

A power management system for a vehicle having wheels and an electric machine operable to provide torque to drive at least one of the wheels includes a first energy storage system capable of supplying power to operate the electric machine. The system also includes a second energy storage system capable of supplying power directly to at least one vehicle load at a lower voltage than the first energy storage system. A voltage conversion device is operable to reduce a voltage of the power supplied by the first energy storage system to the lower voltage to charge the second energy storage system when the vehicle is in a key-off state.