NOVELTY - The battery unit has a first drawer and a second drawer (110) contained in a housing. Both drawers have first composite connectors secured to a housing side that is almost orthogonal to the direction of insertion of the drawers into the housing. The housing has second composite connectors which mate with the first composite connectors when both drawers are inserted into the housings to connect the communication lines (130) between the assembled battery monitoring device and battery management device (16) and the main-circuit lines between the assembled batteries of the battery modules.    USE - Secondary battery unit used as power supply in smart grids or vehicles such as electric cars.    ADVANTAGE - Uses an assembled battery monitoring unit and battery management unit to inform any higher management device of the reliable connection of the main-circuit lines and communication lines in the battery unit. Prevents erroneous line arrangement in assembling and maintaining the battery unit since the main-circuit lines and communication lines connect the connect the assembled battery monitoring devices to the batter management unit in a simple pattern and the battery units can be assembled easily in safety as the first and second drawers are inserted into the housing. Prevents errors in assembling and maintaining the battery unit since the cables connecting the communication connectors in the battery unit are of the same specification and are simplified in specification, and the first drawers have the same configuration. Suppresses degradation of communication between the assembled battery monitoring devices and battery management unit in the battery unit due to reduced influence of noise and due to the non-adjacent arrangement of the connection bars with respect to the cables. Ensures simplified maintenance work of the battery unit while preventing erroneous line arrangement in the assembly and maintenance of the battery unit.    DETAILED DESCRIPTION - The first drawer holds the battery modules, while the second drawer holds the battery management device. The assembled battery monitoring device is configured to detect the temperature and voltage of each battery cell included in the assembled battery in each battery module. The battery management device is configured to communicate with the battery modules.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic diagram showing the connection configuration of the main-circuit lines and communication lines in the battery unit.    Battery management device (16)    Switch devices (18,19)    Second drawer (110)    Connection bars (120)    Communication lines (130)