A battery system includes a battery module that has a plurality of batteries which are provided with release portions each for releasing internal gas when an internal pressure is increased, and an exhaust portion which is provided with an opening portion and guides gas released from the release portions to the opening portion, a non-resettable switch element which is provided at a position where the guided gas passes in a vicinity of the opening portion, and is changed from a first state preset as one of an opened state and a closed state into a second state as the other one of the opened state and the closed state when a preset reference temperature or higher is reached, and a high-temperature abnormality determination unit which determines that the battery module has an abnormality when the switch element is in the second state.