A battery module for containing a plurality of battery units, the battery module including first and second end plates facing each other; and a side plate, the side plate being for extending across a side of the battery units, and the side plate having a first end coupled to the first end plate and a second end coupled to the second end plate, wherein a work hardening unit is disposed at the second end of the side plate, the work hardening unit being hardened in such a way that the second end of the side plate is bent.