What was found
ORD - EMERGENCY BATTERIES WILL NOT RUN EMERGENCY LIGHTS. REPLACED ALL FOUR BATTERY PACKS 43WL, 61WL, 73WL, AND 62WL. OPS CHECK GOOD. AIRCRAFT WAS RETURNED TO SERVICE. REF: OPERATOR CONTROL NR 97ZZZX4163, 97ZZZX4164, AND 97ZZZX4165. (X)