Abstract: A multi-series battery control system comprises a plurality of unit battery cell of which unit consists of multiple battery cells connected in series; a plurality of control IC comprising a control circuit for controlling the unit battery cell; a main controller that sends and receives signal to/from the control ICs via an insulation; means for sending an abnormality signal, which represents the existence or the absence of abnormality of the control ICs or the battery cells, to the main controller from the control ICs, responding to the first signal outputted from the main controller via the insulation; and means for searching contents of the abnormality in the control ICs or the battery cells and sending the abnormality contents signal based on the search, to the main controller from the control ICs, responding to the second signal outputted from the main controller via the insulation.