As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
INFLIGHT THE EMERGENCY LIGHTS OVER L1 AND R1 REMAINED ON. ALL OTHERS OFF PER FLIGHT DECK SWITCH POSITION. CONFIRMED FWD LEFT EPSU FAILED ON CIDS EMERGENDY LIGHT SYSTEM TEST. REMOVED AND REPLACED EPSU BASE ASSY. REINSTALLED OLD BATTERY ON NEW UNIT. ACCOMPLISHED IAW AMM 33-51-38 CIDS TEST PASSED. OK FOR SERVICE.