A battery pack, comprising: a case; and a battery module assembly being arranged in the case, comprising: at least two battery modules arranged along a first direction, each of the battery modules comprising a plurality of battery cells, and a shell side wall of the battery cell comprising two oppositely arranged first side walls and two oppositely arranged second side walls, wherein an area of the first side wall is larger than that of the second side wall, and the first side wall is perpendicular to the first direction; and a cooling plate arranged between two adjacent battery modules to perform heat exchange with the first side walls of the battery cells of the two adjacent battery modules; wherein the battery pack comprises at least two said battery module assemblies, and the at least two battery module assemblies are arranged along a direction perpendicular to the first direction; and characterised in that the two cooling plates corresponding to the two adjacent battery module assemblies are arranged separately; or the two cooling plates corresponding to the two adjacent battery module assemblies are connected by the connecting portion; and the case comprises a separator beam, the separator beam is fixedly connected to the case side wall, the separator beam divides internal space of the case into a plurality of subspaces, and the at least two battery module assemblies are respectively arranged in the plurality of subspaces. a case; and a battery module assembly being arranged in the case, comprising: at least two battery modules arranged along a first direction, each of the battery modules comprising a plurality of battery cells, and a shell side wall of the battery cell comprising two oppositely arranged first side walls and two oppositely arranged second side walls, wherein an area of the first side wall is larger than that of the second side wall, and the first side wall is perpendicular to the first direction; and a cooling plate arranged between two adjacent battery modules to perform heat exchange with the first side walls of the battery cells of the two adjacent battery modules; wherein the battery pack comprises at least two said battery module assemblies, and the at least two battery module assemblies are arranged along a direction perpendicular to the first direction; and characterised in that the two cooling plates corresponding to the two adjacent battery module assemblies are arranged separately; or the two cooling plates corresponding to the two adjacent battery module assemblies are connected by the connecting portion; and the case comprises a separator beam, the separator beam is fixedly connected to the case side wall, the separator beam divides internal space of the case into a plurality of subspaces, and the at least two battery module assemblies are respectively arranged in the plurality of subspaces. at least two battery modules arranged along a first direction, each of the battery modules comprising a plurality of battery cells, and a shell side wall of the battery cell comprising two oppositely arranged first side walls and two oppositely arranged second side walls, wherein an area of the first side wall is larger than that of the second side wall, and the first side wall is perpendicular to the first direction; and a cooling plate arranged between two adjacent battery modules to perform heat exchange with the first side walls of the battery cells of the two adjacent battery modules; wherein the battery pack comprises at least two said battery module assemblies, and the at least two battery module assemblies are arranged along a direction perpendicular to the first direction; and characterised in that the two cooling plates corresponding to the two adjacent battery module assemblies are arranged separately; or the two cooling plates corresponding to the two adjacent battery module assemblies are connected by the connecting portion; and the case comprises a separator beam, the separator beam is fixedly connected to the case side wall, the separator beam divides internal space of the case into a plurality of subspaces, and the at least two battery module assemblies are respectively arranged in the plurality of subspaces.