As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS IN BASE MAINTENANCE: WELS CONTROL UNIT BATTERY POWER SHOWS A MAINTENANCE MESSAGE 33-11420. REMOVED AND REPLACED WELS BATTERY UNIT FROM THE WELS CONTROL UNIT (M3351092) IN THE STOW BIN 26H IAW AMM DMC-B787-A-33-51-07-02B-520A-A.