A power manager includes a converter and a controller. The converter is coupled between first and second energy storage devices, and the controller controls transfer of power between the first and second energy storage devices through the converter. The first energy storage device is to supply power to a first power subsystem of an electronic device, and the second energy storage device is to supply power to a second power subsystem of the electronic device. The subsystem may have different operating voltage requirements. When a level of the second battery falls below a first reference value, the controller controls the transfer of power from the first energy storage device to the second energy storage device. A transfer of power in a reverse direction may occur when a level of the first energy storage device falls below a second reference value.