As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU WILL NOT START. HANGS BETWEEN 25 AND 35 PERCENT RPM AND SHUTS DOWN WITH FAULT LIGHT ON. CREW COMMENTS: STARTED ON SECOND ATTEMPT. NOTED APU BAT TOOK EXCESSIVELY LONG TO FULLY RECHARGE AFTER START AND BAT DRAWS DOWN TO 14V DURING CRANK. BAT WEAK AND NEEDS REPLACED. REPLACED BATTERY. APU CRANK VOLTAGE CHECKS GOOD AND APU ACCELL AND START CHECKS GOOD.