What was found
EMER LIGHTS COMPLETELY DEAD. WE CHARGED THE BATT PACKS FOR 45 MINS ON THE APU AND RETESTED. NOT A SINGLE LIGHT CAME ON IN THE ON POSITION. ACCESSED CLOSEOUT PANEL TO THE LEFT AFT CLOSET ASSEMBLY AND REMOVED FAULTY #4 BATT PACK P/N CBS28-1 S/N 5792M, INSTALLED CUSTOMER SUPPLIED REPAIRED #4 BATT PACK P/N CBS28-1 S/N 006544 PERFORMED OPERATIONAL CHECK, ALL CHECKS GOOD NO FAULT FOUND, REINSTALLED ALL ACCESS GAINED AND RETURNED AIRCRAFT TO INITIAL CONDITION, REF CE 680 A AMM 33-50-06, 33-50-00