A battery module for use in an electric vehicle is disclosed. The battery module includes a plurality of cells arranged in a predetermined pattern within the module. The battery module also includes an optical pyrometer arranged inside the module. The optical pyrometer is installed within the module after being tuned to detect a predetermined frequency or band of frequencies. The pyrometer will be used to detect an increase in short wave radiation density from one of the battery cells within the module wherein that battery cell has a temperature above a predetermined threshold. The optical pyrometer will be used to communicate an electric signal to a control system of the electric vehicle wherein that control system will implement a predetermined mitigation process to contain the thermal event of that one cell within the battery module.