A system and method are disclosed for providing a high efficiency bypass circuit for multi-stage direct current to direct current (DC-DC) converters used in battery powered systems. When the system is operating in a battery mode, the vehicle power source is unplugged from the power supply input connector and the external battery is connected in its place. The system uses a relay to bypass the flyback converter so as to connect the boost converter output directly to the output terminals. The system uses a single control signal to: 1) energize the relay connecting the boost converter output directly to the output terminals, 2) adjust the boost converter circuit to cause the boost converter to deliver a voltage equal to what the flyback converter would have delivered, and 3) disable the flyback converter.