POWER SUPPLY DEVICE AND METHOD

A power supply device includes a first battery and a second battery, and a first switching unit, configured to select the first battery to supply power to a load; a second switching unit, configured to select the second battery to supply power to the load; a processing unit, configured to detect power of the first battery and the second battery; when the power of the second battery is greater than a first preset value, the processing unit disconnects the first switching unit and turns on the second switching unit to enable the second battery to supply power to the load; the processing unit controls the second battery to charge the first battery when the power of the first battery is less than a second preset value; and when the power of the first battery is greater than a third preset value, the second battery stops charging the first battery.