Disclosed is a battery system wherein safety of a lithium secondary battery can be enhanced by efficiently deactivating (inactivating) lithium metal deposited on a negative electrode of the lithium secondary battery. Also disclosed is an automobile. Specifically disclosed is a battery system comprising a lithium ion secondary battery and a temperature control unit for controlling the temperature of the lithium ion secondary battery. The temperature control unit performs such a control that the temperature T of the lithium ion secondary battery is maintained within the following range: 55° C.