A battery system improving operation reliability of a swelling current interrupt device (CID) is provided. The battery system includes a cooling plate that forms an appearance of a battery in which the swelling CID interrupting a current flow is mounted and includes a swelling aperture formed therein. The swelling aperture induces an expansion of a pouch in which the swelling CID is embedded. Therefore, since the swelling aperture is formed in the cooling plate, improved operation reliability of the swelling CID than a battery system according to related art in which operation reliability was varied based on a thickness of a pouch cell is obtained.