A battery pack and a method for controlling the same are disclosed. In one aspect, the battery pack includes a master battery management system (BMS) and a plurality of battery modules each including a slave BMS connected to the master BMS. In another aspect, the method includes first determining the number of slave BMS′ electrically connected to the master BMS, receiving a plurality of voltage values of the battery modules from the slave BMS′ and first calculating an average value of the voltage values. The method also includes second determining a terminal voltage of the battery pack, comparing the average voltage value with the terminal voltage of the battery pack to calculate the number of the battery modules connected in series, and third determining a first series connection relationship of the battery modules, in one of a plurality of serial unit sets, based on the comparison.