An exemplary notebook computer includes a smart battery, a number of status indicator lights, a function key and a control unit electrically coupled to the smart battery, the status indicator lights and the function key. In the condition that the notebook computer is situated either in a shutdown mode or in a power saving mode and the function key is pressed, the control unit reads the data of the remaining capacity of the smart battery through a bus between the smart battery and the control unit so as to calculate the remaining capacity of the smart battery. Thus, the control unit can control the status indicator lights to be light on/off to display the information of the remaining capacity of the smart battery.