A battery pack including a plurality of battery arrays, each battery array including unit batteries that each have a terminal, the plurality of battery arrays being stacked in a first direction; an insulator on at least one side of the battery arrays, terminals of the unit batteries being on the one side; and a sensing bar on the insulator, wherein the insulator includes at least one opening therein, at least one terminal being exposed through the at least one opening, and the sensing bar is electrically connected to the at least one terminal exposed through the at least one opening to sense a state of the battery array.