An electronic system includes a first device and a second device is provided. The first device includes a power connector, a first connector, a first battery, and a charging controller. The second device includes a second connector and a second battery. The power connector is configured to receive an external voltage. The first battery is electrically connected to the power connector and the first connector. The charging controller is electrically connected to the power connector and the first battery. The second connector is utilized for connecting the first connector. The second battery is electrically connected to the second connector. When the first connector is connected to the second connector, the charging controller selectively connects the first battery and the second battery in a series via the first connector and the second connector according to the level of the first battery and the second battery.