As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE FLIGHT CREW REPORTED THE EMERGENCY STANDBY BATTERY FAILED TO TEST DURING PREFLIGHT CHECKS. THE MAINTENANCE PROVIDER TROUBLESHOT AND REMOVED THE EMERGENCY STANDBY BATTERY AND INSTALLED AN INSPECTED / TESTED STANDBY BATTERY. OPS CHECKS WERE PERFORMED AND FOUND SATISFACTORY. THE AIRCRAFT WAS RETURNED TO SERVICE.