A mobile terminal device and method are provided for displaying remaining battery capacity. The device and method comprise internal and external batteries installed on the mobile terminal, a display unit displaying remaining battery capacity, a battery detecting unit identifying whether the external battery is additionally installed, a remaining battery capacity measuring unit measuring total recharged voltage of the internal and external batteries and a control unit displaying the total remaining battery capacity on the display unit corresponding to the measured total recharged voltage. Accordingly, a user may identify installation of the external battery more easily and avoid confusion due to rapid display changes in remaining battery capacity displayed as a recharged voltage difference between the internal and external batteries.