A power management circuit for a battery cell coupled to a load through an output terminal comprising: a current detection circuit configured to detect a discharge current of the battery cell when the battery cell is discharged through the load to generate a discharge-current signal; a loading determination circuit configured to determine a loading value of the load according to the discharge-current signal and a default capacity of the battery to generate a loading signal; and a voltage determination circuit configured to receive the loading signal and determine a cut-off voltage (Vcutoff) of the battery cell according to the loading signal, wherein when the battery voltage of the battery cell drops to the cut-off voltage, the power management circuit is configured to terminate the discharge of the battery cell through the load, wherein when the battery cell is discharged through the load, the voltage determination circuit is configured to perform a comparison operation at each predetermined interval to compare the loading value with at least one loading threshold and generate a comparison result, wherein each time that the comparison result is generated, the voltage determination circuit is configured to determine a voltage value according to the corresponding comparison result, wherein each time that the voltage value is determined, the voltage determination circuit is configured to determine whether a state value representing a relative state-of-charge (RSOC) of the battery cell is smaller than or equal to a first state threshold, and wherein when the state value is smaller than or equal to the first state threshold, the voltage determination circuit is configured to set a level of cut-off voltage to be equal to the determined voltage value. a current detection circuit configured to detect a discharge current of the battery cell when the battery cell is discharged through the load to generate a discharge-current signal; a loading determination circuit configured to determine a loading value of the load according to the discharge-current signal and a default capacity of the battery to generate a loading signal; and a voltage determination circuit configured to receive the loading signal and determine a cut-off voltage (Vcutoff) of the battery cell according to the loading signal, wherein when the battery voltage of the battery cell drops to the cut-off voltage, the power management circuit is configured to terminate the discharge of the battery cell through the load, wherein when the battery cell is discharged through the load, the voltage determination circuit is configured to perform a comparison operation at each predetermined interval to compare the loading value with at least one loading threshold and generate a comparison result, wherein each time that the comparison result is generated, the voltage determination circuit is configured to determine a voltage value according to the corresponding comparison result, wherein each time that the voltage value is determined, the voltage determination circuit is configured to determine whether a state value representing a relative state-of-charge (RSOC) of the battery cell is smaller than or equal to a first state threshold, and wherein when the state value is smaller than or equal to the first state threshold, the voltage determination circuit is configured to set a level of cut-off voltage to be equal to the determined voltage value.