A power management unit (PMU) for supplying electrical energy to a circuitry of a portable electronic device includes a power supply module, a power detection module connected to the power supply module, and a power control module connected to the power detection module and the circuitry. The power supply module includes a battery, a charge controller, and an adapter. The power detection includes a detection resistor connected to the battery, the charge controller, and the adapter. The battery or the adapter provides electrical energy to the circuitry. The adapter further charges the battery to charge the battery when it is used to provide electrical energy to the circuitry. The charge controller detects the current for charging the battery via the detection resistor, and regulates the current for charging the battery when the charging current exceeds a predetermined value.