As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING DAILY INSP OF ACFT, GPU USED. ACFT KEY TURNED (ON) TO CHARGE BATTERIES. APPROX. 2.5 HRS LATER, VENTING OF BATTERY NOTICED FROM ACFT. SMELL OF BURNING PLASTIC. GPU DISCONNECTED, KEY (OFF). ACFT MOVED OUTSIDE. AIRPORT FIRE DEPT. REMOVED NR 1 BATTERY AND ALLOWED TO COOL. THERMAL RUNAWAY ALONG WITH GPU PRODUCING 30 VOLTS NOT 28.8 V.