As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING APU START CYCLE WITH GROUND POWER CONNECTED AND POWERING ACFT, BATTERY DISCHARGE LIGHT ILLUMINATED WITH ASSOCIATED DROP IN DC VOLTAGE. AUX BATTERY DROPS TO APPROX 22 VDC AND THEN RECOVERS APPROX 10 SECONDS AFTER THE APU START CYCLE IS COMPLETE. ACFT GROUNDED. REMOVED STARTER GENERATOR IAW 49-41-21-000-801 AND INSTALLED SERVICEABLE STARTER GENERATOR IAW 49-41-21-400-801. APU STARTING AND OPS TESTED IAW 49-11-00-860-801, GOOD. NO LEAK NOTED.