A dockable device and a power method thereof are provided. The dockable device includes a main device, a main device battery, a connector, a switch and a voltage down-converter. The connector may be coupled to a docking device. The switch, coupled to the main device battery, is configured to be closed to provide power to the main device from the main device battery. The voltage down-converter is configured to provide power with a backup voltage to the main device, wherein the backup voltage is less than a discharge voltage output by a fully discharged main device battery.