Abstract: A vehicle power supply backup system includes a first vehicle battery, a second vehicle battery, a switch, and a controller. The first vehicle battery is configured to output electricity that has a first nominal voltage and that is used to supply electrical power to a first vehicle component. The second vehicle battery has multiple battery cells, and is configured to output electricity that has a second nominal voltage that is higher than the first nominal voltage. The switch is coupled between the first vehicle component and a designated subset of battery cells, which include one or more of the multiple battery cells of the second vehicle battery. The controller is configured so that when a backup condition of the first vehicle battery is detected, the switch is changed to the second state thereby causing the designated subset of battery cells to supply electricity to at least the first vehicle component.