BATTERY PACK

Object [0002] To provide a technique in which the likelihood of mispositioning between an upper-part case and a cell case of a battery pack can be reduced. [0003] Solution [0004] A battery pack (2; 402; 602) includes an outer case (12; 412; 612), which comprises an upper-part case (14; 414) and a lower-part case (15; 415) fixed to the upper-part case (14; 414), and a cell case (80; 480; 780; 980), which is housed in the outer case (12; 412; 612). An engaging part (30) is provided on one of the upper-part case (14; 414) and the cell case (80; 480; 780; 980). An engaged part (110), with which the engaging part (30) engages, is provided on or in the other of the upper-part case (14; 414) and the cell case (80; 480; 780; 980).