As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED MAIN BATTERY OVER HEAT LIGHT CAME ON IN FLIGHT. BATTERY WAS CHECKED AFTER LANDING AND WAS NOT WARM. BATTERY CELLS CHECKED GOOD ND WERE ALL EVEN VOLTAGE. THE BATTERY OVERHEATED SENSOR WAS FOUND TO BE DEFECTIVE. PURCHASED NEW BATTERY AND SENSOR.