What was found
EMER LIGHTS WILL NOT COME ON WHEN SWITCH SELECTED TO ON WITH ACFT POWERED DOWN. PREFLIGHTED WITH THE AIRPLANE POWERED UP, THEN POWERED DOWN TO WAIT. AFTER POWERING DOWN, I CHECKED THE EMER LIGHTS AND FOUND NORMAL OPERATION. AFTER WAITING AN HOUR, WE CAME OUT TO POWER UP, AND TESTED EMER LIGHTS AGAIN AND FOUND THAT WITH AIRCRAFT POWER OFF, THE EMER LIGHTS WOULD NOT WORK WHEN SELECTED TO ON. THEY WOULD WORK WHEN SELECTED TO ARM. WHEN THE AIRCRAFT WAS POWERED UP, THE LIGHTS WOULD WORK IN BOTH ON AND ARM. REMOVED AND REPLACED #4 EMERGENCY LIGHT BATTERY PACK IAW CE·680A MM 33-50-06, PERFORMED OPERATIONAL TEST, NO DEFECTS NOTED.