What was found
DURING CRUISE FLIGHT AT FL430, WE EXPERIENCED A MASTER WARNING FOR A NR 1 BATTERY OVER TEMPERATURE. THE TEMPERATURE WAS INDICATING 63 DEGREES C. THE EMERGENCY PROCEDURE CHECKLIST WAS PERFORMED. THE TEMPERATURE CONTINUED TO CLIMB OVER AN APPROXIMATELY A 10 MINUTE PERIOD TO 65 DEGREES CELSIUS. AT THAT TIME, A CREW DECISION WAS MADE TO DIVERT. MAINTENANCE REPLACED THE LEFT AIRCRAFT MAIN BATTERY. OPERATIONAL CHECKS PERFORMED WITH NO DEFECTS NOTED. AIRCRAFT WAS RETURNED TO SERVICE.