As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON RETURN FLIGHT, SULFUR LIKE FUMES WERE COMING FROM THE AIR CONDITIONER VENTS. SMELL WENT AWAY WHEN THE AIR CONDITIONER IS TURNED OFF. LT SYS OFF & COMPLETED FLIGHT WITHOUT INCIDENT. INSPECTED ACFT & NOTICED ACFT BATTERY VERY HOT & THE SULFUR SMELL IS FROM BATTERY. REPLACED BATTERY, ALL CHECKED GOOD. ACFT RETURNED TO SERVICE.