Provided is a battery pack, which has a reduced number of embedded components so as to have reduced cost and weight and has an efficiently adjusted internal temperature so as to have improved performance and stability, the battery packing including: a lower case including a first lower side wall extending from a bottom surface, and a second lower side wall and a third lower side wall respectively connected with the first lower side wall and arranged so as to face each other, wherein the side facing the first lower side wall is open; a battery unit accommodated in the lower case and including a plurality of battery cells; and an upper case arranged to face the lower case so as to seal the battery unit.