As automotive industry continues its embrace of high capacity Li-ion batteries, increasing safety monitoring measures are needed. The use of Li-ion battery in electric vehicles presents itself far more strenuous conditions than other applications such as cell phones, cameras, computers and other stationary applications. Not only the power requirements for electric vehicles are high but also the operating environment is much more uncertain due to temperature variability, vibration, high rates of charge and discharge. To dissipate heat away from batteries, cooling loop of water is used. To protect a battery bank from failure, effective thermal management is absolutely essential. To this end, we have developed a temperature monitoring method which supplement existing function of cooling with that of temperature monitoring. We have achieved this by introducing aqueous based redox couple potassium ferri/ferro cyanide in water and using graphite electrodes in the path of flowing electrolyte. The ions reduce/oxidize based on temperature and produce voltage proportional to temperature difference. As a result, we are able to obtain temperature profile of the entire cooling loop and provide additional information to battery management system for reliable operation.