A battery pack, comprising: a plurality of battery cells, wherein each of the plurality of battery cells comprises a top cover and a case, the top cover is hermetically connected on a top of the case, the case comprises opposite first surfaces and opposite second surfaces, and an area of each first surface is larger than that of each second surface; a lower housing, comprising a bottom plate disposed at a bottom, side plates disposed at sides, an opening disposed at an upper part; each of a pair of opposite side plates of the lower box is disposed with a reinforcing beam; at least one first surface of the plurality of battery cells is in contact with a side plate of the lower housing or the reinforcing beam; at least one cross beam, fixedly connected to the side plates of the lower housing or the reinforcing beam at both ends of the at least one cross beam, and configured to divide an internal space of the lower housing into at least two battery regions, such that the battery cells are arranged in rows in the lower housing, wherein, the at least one cross beam is perpendicular to the reinforcing beam; and the reinforcing beam, comprising: a first reinforcing beam disposed inside the lower housing, wherein, for the two outermost battery cells in a row, at least one first surface of the plurality of battery cells is in contact with the first reinforcing beam; a third reinforcing beam disposed inside the lower housing and located on the at least one cross beam, the third reinforcing beam is perpendicular to the at least one cross beam; wherein, a bulge is disposed at each of two ends of the at least one cross beam, a groove is provided at a position on the third reinforcing beam, the position corresponding to the bulge of the at least one cross beam, and the bulge at each end of the cross beam is snap-fitted into the groove of the third reinforcing beam. a plurality of battery cells, wherein each of the plurality of battery cells comprises a top cover and a case, the top cover is hermetically connected on a top of the case, the case comprises opposite first surfaces and opposite second surfaces, and an area of each first surface is larger than that of each second surface; a lower housing, comprising a bottom plate disposed at a bottom, side plates disposed at sides, an opening disposed at an upper part; each of a pair of opposite side plates of the lower box is disposed with a reinforcing beam; at least one first surface of the plurality of battery cells is in contact with a side plate of the lower housing or the reinforcing beam; at least one cross beam, fixedly connected to the side plates of the lower housing or the reinforcing beam at both ends of the at least one cross beam, and configured to divide an internal space of the lower housing into at least two battery regions, such that the battery cells are arranged in rows in the lower housing, wherein, the at least one cross beam is perpendicular to the reinforcing beam; and the reinforcing beam, comprising: a first reinforcing beam disposed inside the lower housing, wherein, for the two outermost battery cells in a row, at least one first surface of the plurality of battery cells is in contact with the first reinforcing beam; a third reinforcing beam disposed inside the lower housing and located on the at least one cross beam, the third reinforcing beam is perpendicular to the at least one cross beam; wherein, a bulge is disposed at each of two ends of the at least one cross beam, a groove is provided at a position on the third reinforcing beam, the position corresponding to the bulge of the at least one cross beam, and the bulge at each end of the cross beam is snap-fitted into the groove of the third reinforcing beam. a first reinforcing beam disposed inside the lower housing, wherein, for the two outermost battery cells in a row, at least one first surface of the plurality of battery cells is in contact with the first reinforcing beam; a third reinforcing beam disposed inside the lower housing and located on the at least one cross beam, the third reinforcing beam is perpendicular to the at least one cross beam; wherein, a bulge is disposed at each of two ends of the at least one cross beam, a groove is provided at a position on the third reinforcing beam, the position corresponding to the bulge of the at least one cross beam, and the bulge at each end of the cross beam is snap-fitted into the groove of the third reinforcing beam.