Patent ID: 8808890

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, the optical fiber including a core, a clad that covers an outer side of the core, and a covering layer that covers an outer side of the clad, wherein the core is formed of a material having a refractive index higher than that of the clad; a detector including a photodiode that receives the laser beam transmitted via the optical fiber and converts the received laser beam into an electronic signal and a control circuit that detects abnormality of the lithium ion battery from the electronic signal on the basis of an absolute value of a transmission loss of the laser beam caused by lateral pressure acting on the optical fiber; an alarm that warns, when abnormality of the lithium ion battery is detected by the detector, a user of the abnormality; a first reinforcement layer that covers an outer side of a portion of the optical fiber that extends between the laser beam source and the lithium ion battery; and a second reinforcement layer that covers an outer side of a portion of the optical fiber that extends between the lithium ion battery and the detector, wherein: the laser beam source that emits the laser beam is located at a first end of the optical fiber, and the detector that receives the laser beam is located at a second end of the optical fiber; and a reinforcement layer is absent from a portion of the optical fiber that is wound around the outer circumferential portion of the lithium ion battery.