The invention relates to a control system for a battery assembly and a method of determining reuse of the battery assembly. The control system for the battery assembly (2) that consists of a plurality of batteries (11A, 11B, 11C, 11N) determines whether the battery assembly (2) can be reused, by using detected values of the open voltage, internal resistance and full charge capacity of each of the batteries (11A, 11B, 11C, 11N), as evaluation parameters.