As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON FLIGHT 3999 THE CREW REPORTED AN ABNORMAL ELECTRICAL PROBLEM. THE BATTERIES ON THE AIRCRAFT WENT INTO AN ESSENTIAL TRANS MODE. (IE- PLANE GOES DARK AND EICAS ONLY). THE CAPTAIN ELECTED TO RETURN TO FAR. THE AIRCRAFT LANDED WITHOUT INCIDENT. THE AIRCRAFT WAS REMOVED FROM SERVICE. FOUND BAD BATTERY 1 SWITCH. REMOVED AND REPLACED THE ELECTRICAL CONTROL PANEL IAW EMB-145 AMM 24-00-01. THE OPERATIONAL CHECK WAS GOOD PER EMB-145 AMM 24-60-00. THE AIRCRAFT WAS RETURNED TO SERVICE.