Lower order control devices control plural battery cells configuring
plural battery modules. An input terminal of the low order control device
in the highest potential, an output terminal of the low order control
device in the lowest potential, and a high order control device are
connected by isolating units, photocouplers. Diodes which prevent a
discharge current of the battery cells in the battery modules are
disposed between the output terminal of the low order control device and
the battery cells in the battery module on the low potential side.
Terminals related to input/output of a signal are electrically connected
without isolating among the plural low order control devices.