As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED. DURING CIDS 1 SYSTEM TEST, EMERGENCY POWER SUPPLY UNIT (14WL) MID R/DEU B (300RH4) MESSAGE APPEARED. REPLACED EMERGENCY POWER SUPPLY UNIT (14WL) BATTERY ON MCM CARD 2735. OPERATIONS CHECK GOOD. NO FAULTS NOTED.