A battery system for a vehicle includes: a battery module including a plurality of secondary battery cells; a gas sensor; and a housing accommodating the battery module and the gas sensor. At least a portion of an exterior surface of the battery module and/or at least a portion of an interior surface of the housing is covered by a coating. The coating is configured to emit a gaseous species when a temperature exceeds a reference temperature, and the gas sensor is configured to detect the gaseous species.