What was found
AIRCRAFT WAS GROUNDED: WHILE AT THE GATE THE CREW REPORTED HEARING A LOUD BANG / POP FOLLOWED BY AN ELECTRICAL SMELL. PASSENGERS AND THE CREW EVACUATED THE AIRCRAFT VIA THE MAIN CABIN DOOR SAFELY AND FIRE TRUCKS RESPONDED AS A PRECAUTION. (NOTE: NO SLIDES WERE DEPLOYED.). MAINTENANCE FOUND THE LEFT HAND OVERWING EMERGENCY LIGHT POWER SUPPLY BATTERY HAD OVERHEATED AND EXPLODED AND DISCONNECTED IT. THE EMERGENCY POWER SUPPLY UNIT WAS REPLACED AND A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED PER AMM 33-51-38.