As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU FAILED TO START. FAULT LGT ILLUM AND EICAS MSG. APU FAULT DISPLAYED. SECOND ATTEMPT INDICATES (SLOW ACCEL, HUNG START). CREW COMMENTS: APU FAULT AFTER LANDING. APU BAT VOLTS AT 15V. REPLACED APU BATTERY PER MM, GROUND CHECKED NORMAL.