As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAKEOFF, CREW NOTICED RISE IN BATTERY NR 2 TEMPERATURE, FOLLOWED CHECKLIST ISOLATING NR 2 BATTERY. CREW CONTINUED WITH TAKEOFF WITHOUT INCIDENT. BATTERY TEMPERATURE CONTINUED TO RISE, CREW MADE THE DECISION TO RETURN TO DEPARTURE, DECLARING AN EMERGENCY SITUATION. ONCE ON THE GROUND FIRE PERSONNEL TEMPERATURE CHECKED THE BATTERY AT 77F. AT THIS TIME IT WAS NOTED AS A FAILURE OF THE TEMPERATURE SENSOR IN THE BATTERY CASE.