As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BATTERY DISCHARGE LIGHT ILLUMINATED. GROUNDED - YES. M5 BAT CHARGER STATUS LIGHTS OFF. CONFIRMED CORRECT VOLTAGE @ D42 PINS 10, 7, AND 4. P92 C809 CYCLE NO HELP. REMOVED AND REPLACED MAIN BATTERY CHARGER (M5) PER B737-900 AMM 24-31-21.