A system for monitoring a battery module having a plurality of cells includes a sensor adapted to obtain respective cell voltages of the plurality of cells. The controller is adapted to receive data from the sensor, the controller having a processor and tangible, non-transitory memory on which instructions are recorded. The controller is configured to sort the respective cell voltages to create a voltage ranking. The voltage ranking is repeated with at least one new set of cell voltage readings obtained at a predefined checking frequency. Differences in the voltage ranking of the plurality of cells are analyzed. The controller is adapted to control operation of the battery module based in part on differences in the voltage ranking. The controller may be adapted to predict likelihood of a thermal runway event based in part on the differences in the voltage ranking.