As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: WHILE ACCOMPLISHING EMERGENCY POWER SUPPLY UNIT SYSTEM TEST, RECEIVED MESSAGE BATTTERY/EMERGENCY POWER SUPPLY UNIT (13WL) AFT LEFT. ATTEMPTED AFT BATTERY RESET, NO HELP. MAINTENANCE REPLACED EMERGENCY POWER SUPPLY UNIT BATTERY 13WL AFT LEFT PER AMM 33-51-38. OPS CHECK GOOD.