A battery charger includes a battery voltage detector for detecting the voltage of a secondary battery and a battery temperature sensor for detecting the temperature of the secondary battery. A controller determines the voltage of the secondary battery prior to beginning the charging process based on output from the battery voltage detector. The controller also determines the charging level from among a plurality of levels that indicate how much time is required for the secondary battery to reach a full charge, based on the determined voltage of the secondary battery and output from the battery temperature sensor. A display is provided for displaying the charging level that indicates the time remaining to achieve a full charge.