What was found
AIRCRAFT WAS ON FINAL APPROACH TO AIRPORT WHEN BATTERY OVER TEMP LIGHT ILLUMINATED. PILOT TURNED OFF GENERATOR SYSTEM AND LANDED. THE BATTERY WAS DISCONNECTED AND ALLOWED TO COOL. BATTERY WAS REPLACED WITH A SERVICEABLE UNIT. INSPECTION OF REMOVED BATTERY INDICATED LOW WATER LEVELS AND ONE DEAD CELL. AIRCRAFT HAD SAT FOR SEVERAL MONTHS WITHOUT BEING OPERATED, THEN RETURNED TO HEAVY, DAILY USAGE. RECOMMEND MORE FREQUENT CONDITION CHECKS OF BATTERIES INSTALLED IN AIRCRAFT.