A charger integrated circuit for charging a battery device including a first battery and a second battery includes; a first charger configured to generate a first charging current from an input voltage when the input voltage is received from an input voltage terminal, and a battery switch configured to provide the first charging current to the battery device, the battery switch comprising a plurality of transistors for connecting the first battery and the second battery in series or in parallel based on the input voltage, a first both-end voltage of the first battery and a second both-end voltage of the second battery.