A power supply unit for mobile terminals, comprising - a battery, - a power supply conversion module, - a charging management module and - a power supply switching module; wherein - said charging management module and power supply switching module both comprise a power supply input port for connection with an external power supply; - said charging management module is connected with the battery and is adapted for charging the battery when an external power supply is connected; - said power supply conversion module is connected with said power supply switching module and is adapted for converting the voltage of the external power supply into power supply voltage required by the mobile terminal and for controlling on-off state of said power supply switching module such that the power supply switching module is in an on state when no external power supply is connected and the battery supplies power to the mobile terminal, and such that said power supply switching module is off and said power supply conversion module outputs the power supply voltage to the mobile terminal when an external power supply is connected, - wherein said power supply switching module comprises a second resistor, a third resistor and a field effect transistor, said second resistor and third resistor are connected in series to form a voltage sampling circuit, one end of said third resistor is connected with said power supply conversion module, a voltage dividing point of said voltage sampling circuit is connected with a gate of said field effect transistor, a source of said field effect transistor is connected with said battery, and a drain of said field effect transistor is connected for supplying power to the mobile terminal; and - wherein the power supply conversion module comprises an output port for supplying the power supply voltage to the mobile terminal and the third resistor of the power supplying switching module is connected to that output port. - a battery, - a power supply conversion module, - a charging management module and - a power supply switching module; wherein - said charging management module and power supply switching module both comprise a power supply input port for connection with an external power supply; - said charging management module is connected with the battery and is adapted for charging the battery when an external power supply is connected; - said power supply conversion module is connected with said power supply switching module and is adapted for converting the voltage of the external power supply into power supply voltage required by the mobile terminal and for controlling on-off state of said power supply switching module such that the power supply switching module is in an on state when no external power supply is connected and the battery supplies power to the mobile terminal, and such that said power supply switching module is off and said power supply conversion module outputs the power supply voltage to the mobile terminal when an external power supply is connected, - wherein said power supply switching module comprises a second resistor, a third resistor and a field effect transistor, said second resistor and third resistor are connected in series to form a voltage sampling circuit, one end of said third resistor is connected with said power supply conversion module, a voltage dividing point of said voltage sampling circuit is connected with a gate of said field effect transistor, a source of said field effect transistor is connected with said battery, and a drain of said field effect transistor is connected for supplying power to the mobile terminal; and - wherein the power supply conversion module comprises an output port for supplying the power supply voltage to the mobile terminal and the third resistor of the power supplying switching module is connected to that output port.