As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER APU START-THE CABIN FILLED UP WITH SMELL OF ELECTRICAL SMOKE & THE PASSENGERS WERE DEPLANED-WITH THE RESULTANT / ""BATTERY CHARGER FAIL"" ALERT. REMOVED & REPLACED BATTERY CHARGER PER B717 AMM 24-34-03 AND REPLACED ALL THREE BATTERIES PER B717 / AMM 24-34-01. ALL RTS PASSED & CHECKS NORMAL. ALSO APU STARTS NORMAL NO DEFECTS NOTED AT THIIS TIME.