As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAIL TO START ON BATTERY GROUNDED - YES. APU "LOW BATTERY VOLTAGE FAIL TO START" MESSAGE 49-41249 ON 17 FAILED STARTS. PERFORMED B737-900 FIM 49-40 TASK 822, PER FIM REMOVED AND REPLACED APU START POWER UNIT REF B737-900 AMM 49-41-71/401. OP CHECK NORMAL.