Patent ID: 8097352

Claim:
A battery system comprising: a lithium ion battery formed in a cylindrical shape and including an organic electrolytic solution as an electrolyte; a laser beam source that emits a laser beam; an optical fiber of a single mode that is wound around an outer circumferential portion of the lithium ion battery in a plurality of lines and via which the laser beam emitted from the light source is transmitted; a housing that houses the lithium ion battery and a region of the optical fiber that is in contact with an outer surface portion of the lithium ion battery and is arranged in contact with the optical fiber, the optical fiber being disposed between the housing and the lithium ion battery, such that when a lateral pressure from the lithium ion battery acts on the optical fiber, the lateral pressure is exerted on a first side of the optical fiber facing the lithium ion battery while a second side of the optical fiber is restrained by the housing; a detector that receives the laser beam transmitted via the optical fiber and detects abnormality of the lithium ion battery on the basis of a change in transmission properties caused by lateral pressure acting on the optical fiber or a change with time of the loss; and an alarm that warns, when abnormality of the lithium ion battery is detected by the detector, a user of the abnormality.