As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT, MAIN BATTERY DISCHARGE STATUS MESSAGE ILLUMINATED. AIRCRAFT RETURNED TO BLOCKS. (BTB). MAINTENANCE REMOVED AND REPLACED MAIN BATTERY CHARGER. OPS CHECKED GOOD IAW AMM 24-31-01-4. ACFT RFEMAINS ETOPS 180. AIRCRAFT RETURNED TO SERVICE.