Traction Battery Controller Utilizing Voltage Rebound of Parallel-Connected Battery Cells to Detect for a Thermal Event

A method for detecting a thermal event of a battery, such as a traction battery of an electrified vehicle, includes monitoring a voltage of a group of parallel-connected cells of the battery. In response to confirming that the voltage of the group has a voltage rebound, a thermal event of the battery is detected. The detection of the thermal event may further depend on detection of a deviation of another operating parameter, such as temperature or pressure, of the battery.