What was found
WITHIN 200' OF LEVELLING AT FL450, BATTERY EXEEDANCE YELLOW CAS. LATER IT EXTINGUISHED. SHORTLY AFTER IT WOULD COME ON & OFF & THEN REMAINED ON, HAD ALREADY BEGUN TO RUN QRH. DIVERTED TO KSTL. BATTERY VOLTAGE ON SCHEMATIC SHOWED 29 V & GEN 1 SHOWED 29.1. HAVE CW FIM 24-36-00-810=802-A & FOUND THE LT GCU WAS CAUSING ISSUE. SWAPPED GCU'S FROM LT AND RT TO VERIFIED LT GCU CAUSING THE ISSUE. SWAPPED BACK TO ORIGINAL POSITION. REMOVED AND AND REPLACED THE LT GCU.