To provide a battery pack in which security is maintained even when an impact is given to it.

Cylindrical secondary batteries 210 are built in the battery pack, in which the adjacent secondary batteries are arranged in an off-set state, and lead plates 240 are formed in a zigzag state so as to be connected to end faces of the batteries 210 arranged in the off-set state. By this, when an external force is applied to the battery pack, a force works in the cylindrical secondary batteries arranged in the off-set state to expand them to a perpendicular direction against the direction of the external force, and when a force exceeding a prescribed limit is applied, a force works so that the connection of the lead plate to the batteries is released and that the batteries are disassembled in the perpendicular direction. By the above, crush of the battery itself is effectively evaded, short-circuits or the like by liquid leakages are prevented, and a safety is maintained even if the battery pack is broken.

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