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 OPERATIONAL TEST OF EMERGENCY LIGHTS, EMERGENCY POWER SUPPLY UNIT SYSTEM TEST GOT FAULT MESSAGE "BAT/EPSU (11WL) EXT L ". PERFORMED BUILT IN TEST EQUIPMENT TEST ON EMERGENCY POWER SUPPLY UNIT "BAT FAULT" MESSAGE. REPLACED EMERGENCY POWER SUPPLY UNIT BATTERY PER AMM 33-51-38.