Patent ID: 7345451

Claim:
A power supply device providing required power to a loading device, the power supply device comprises: a battery used to selectively output required power to the loading device, wherein the battery has a current meter for measuring the current flowing into and from the battery to gauge the power of the battery; an adjustable power converter used to receive and convert an alternating current (AC) voltage into a first direct current (DC) voltage or a second DC voltage outputted to the loading device, wherein the adjustable power converter further receives an adjusting signal then outputs the second DC voltage when the adjusting signal is enabled, the magnitude of the second DC voltage is lower than an end voltage of the battery; and a control circuit coupled to the battery and the adjustable power converter, wherein when the power of the battery is gauged, the adjusting signal is enabled by the control circuit for the adjustable power converter to output the second DC voltage, and the control circuit controls the battery to discharge to the loading device for the current meter to re-gauge the power of the battery.