A battery pack is disclosed. In one aspect, the battery pack includes a chargeable battery and a battery management system (BMS) configured to charge the battery in a plurality of charging periods each including a constant current supply period and a constant voltage supply period. The battery pack also includes a resistance estimator configured to estimate the resistance of the battery. The BMS is further configured to change a charging period of the battery from a constant voltage supply period of an ith charging period to a constant current supply period of an (i+1)th charging period based on the resistance of the battery, and wherein i is a natural number.