An apparatus and a method to charge a battery, the battery charging apparatus including: a battery unit which is chargeable; a battery charging unit which charges the battery unit; and a controller which adjusts a preset charge voltage of the battery unit based on a charge allowance capacity of the battery unit to have a predetermined value, and controls the battery charging unit to output the adjusted charge voltage and to charge the battery unit. Accordingly, the apparatus and method are capable of charging a battery based on a charge allowance capacity decreased owing to deterioration of the battery to safely use the battery and to extend a life of the battery.