a first housing;

a second housing connected to the first housing to be rotatable with respect to the first housing;

a connection terminal disposed in an inner space of the first housing and configured to connect to an external power supply device;

a switching circuit disposed in an inner space of the first housing, the switching circuit comprising an input terminal connected to the connection terminal, a first output terminal, and a second output terminal, is the switching circuit configured to connect the input terminal to the first output terminal or the second output terminal;

a first battery disposed in the inner space of the first housing and connected to the power supply device through the first output terminal;

a second battery disposed in an inner space of the second housing and connected to the power supply device through the first output terminal;

at least one monitoring circuit configured to monitor a voltage of the first battery and a voltage of the second battery;

a charging circuit disposed in the inner space of the first housing and configured to adjust a voltage or a current of power received through the second output terminal and to output the adjusted voltage or current to the first battery and the second battery;

a processor connected to the switching circuit, the at least one monitoring circuit, and the charging circuit, and connected to the power supply device through the connection terminal,

wherein an anode (+) of the first battery is connected to a first power terminal of the connection terminal while the input terminal is connected the first output terminal, a cathode (−) of the first battery is connected to an anode (+) of the second battery through a power line crossing the first housing and the second housing, a cathode (−) of the second battery is connected to a second power terminal of the connection terminal, and an output terminal of the charging circuit is connected to the power line, and

wherein the processor is configured to:

identify whether the power supply device corresponds to a model supporting a function of adjusting a voltage or a current, by performing data communication with the power supply device through the connection terminal;

based on a result of the identification showing that the power supply device corresponds to a model supporting the adjusting function, connect the input terminal to the first output terminal and control the adjusting function of the power supply device;

recognize that a voltage of the first battery or a voltage of the second battery reaches a designated target voltage using data received from the at least one monitoring circuit; and

based on the voltage of the first battery or the voltage of the second battery reaching the designated target voltage, connect the input terminal to the second output terminal and control the adjusting function of the charging circuit.