A plurality of single cells 10a to 10d, each being packaged by laminate
films 12 and 13, are attached onto one surface of a flexible printed
circuit board 20, in a state of being interconnected in series to each
other, by the use of a double faced tape. Single cells 10a' to 10d' are
attached in a similar way onto the other surface of the flexible printed
circuit board 20. Each group of the cells on the both surfaces of the
flexible printed circuit board 20 are interconnected in parallel. Voltage
detection lines 30a to 30e are wired on the flexible printed circuit
board 20. Positive and negative electrode tabs 14 and 15 of the
respective single cells are connected to the respectively corresponding
voltage detection lines 30a to 30e through connection terminals 31a to
31e provided on the flexible printed circuit board 20.