What was found
CABIN EMERGENCY LIGHTING IS NOT WORKING PROPERLY. WITH BATTERIES OFF & FOLLOWING A 30 MIN CHARGE WITH APU ON, EMERGENCY LIGHTS WILL ILLUMINATE IN ON, BUT FAIL TO ILLUMINATE IN ARM. FAILURE DISCOVERED DURING PREFLT WHEN INTERIOR & EXTERIOR EMERGENCY LIGHTS WOULD NOT ILLUMINATE IN EITHER SWITCH POSITION, NOTING ACFT HAD ONLY BEEN OFF FOR APPROX 3 HRS AFTER SEVERAL HOURS OF FLYING. TROUBLESHOT TO FAULTY ELPS NR 4, 3 & 2. REMOVED FAULTY ELPS 4 & INSTALLED NEW ELPS. REMOVED BATTERY PACK & INSTALLED NEW BATTERY PACK. REMOVED BATTERY PACK & INSTALLED NEW BATTERY PACK. POWERED ACFT, PERFORMED OPS CHK OF EMERGENCY LIGHT SYSTEM, OPS CHKD GOOD. WORK DONE IAW AMM 33-53-13, 33-53-09, & 33-53-05. NO DEFECTS NOTED.