Abstract: A cell module assembly includes a plurality of battery cells, each of the battery cells having electrode leads, a case configured to receive the battery cells, a cover plate located at an open upper surface of the case so as to be coupled to the case, and a busbar unit located at the front and the rear of the case, from which the electrode leads of the received battery cells protrude. The case is configured to have a U shape in which a base plate defining a bottom surface of the case and side plates defining opposite side surfaces of the case are coupled to each other, and the busbar unit includes a busbar frame, one side of which is bent, whereby a process of manufacturing the cell module assembly is simplified and the battery cells are easily received in the case.