As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 9603 - BTB - DURING TAXI APU BATTERY CHARGER SPARKED TWICE, THEN STARTED, FILLING THE MAIN CABIN WITH SMOKE UNTIL C/B POPPED. AIRCRAFT RETURNED TO GATE. FOUND APU BATTERY CHARGER DEFETIVE. REPLACED APU BATTERY CHARGER, OPERATIONAL CHECK NORMAL. (M)