Provided is a battery gauging method for a portable terminal including an active matrix organic light emitting diode (AMOLED) display. The battery gauging method may measure a voltage value of a battery, may determine, for each pixel, RGB information associated with image data buffered in a frame buffer, may determine, for each pixel, a preliminary compensation value corresponding to determined RGB information so as to calculate a compensation value by adding preliminary compensation values of all pixels, and then determine a residual quantity of the battery based on the measured voltage value and the compensation value.