A battery thermal event detection system includes a battery, a chemiresistor, and a temperature-sensitive sample in contact with a surface of the battery. The sample is configured to, responsive to a change in battery temperature, release a gas configured to alter a resistance of the chemiresistor. The system further includes a controller coupled with the chemiresistor and configured to, responsive to detecting a change in the resistance greater than a threshold change, reduce power supplied by the battery.