FO sensors, specifically fiber Bragg grating (FBG) sensors, are embedded within the battery cells to measure strain and temperature shifts. A new study by researchers from Palo Alto Research Center (PARC, a Xerox Company) and LG Chem Power presents a novel method for real-time battery monitoring using embedded fiber-optic sensors. The innovative application of fiber sensors allows for spatially resolved temperature. The interaction between a fibre optic evanescent wave sensor and the positive electrode material, lithium iron phosphate, in a battery cell is presented. The optical–electrochemical combination was investigated in a reflection‐based and a transmission‐based configuration, both leading to comparable.