Secondary battery unit

According to one embodiment, a unit includes battery modules each including an assembled battery including battery cells and a monitoring device, a BMU to communicate with the battery modules, a first drawer holding the battery module, a second drawer holding the BMU, and a housing containing the first drawer and the second drawer. The first and second drawers include first composite connectors secured to a side of the housing, which is almost orthogonal to a direction in which to insert the drawers into the housing. The housing has second composite connectors which mate with the first composite connectors, thereby to connect communication lines between the monitoring device and the BMU and the main-circuit lines between the assembled batteries of the battery modules.