As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED AND IS IN CHECK FOR SCHEDULED MX. DURING THE PRE-HANGAR CHECKS THE EPSU SYSTEM TEST GIVES THE MAINTENANCE MESSAGE: BAT/EPSU (11WL) EMER. LIGHT NEED TO BE TROUBLESHOOTED AS PER TSM 33-51-00-810-855-A REV. 97. REPLACED EPSU BATTERY (11WL) AS PER AMM 33-351-38-400-002-A REV. 97. MX ACTION IS ACCEPTABLE.