As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE FLIGHT CREW REPORTED THAT THE STANDBY ELECTRICAL POWER FAILS PREFLIGHT TESTS. THE MAINTENANCE TEAM TROUBLESHOT AND DETERMINED THAT THE LEFT STANDBY BATTERY WAS DEFECTIVE AND WAS REPLACED WITH A INSPECTED/TESTED UNIT. OPS CHECKS WERE SATISFACTORY, AND THE AIRCRAFT WAS RETURNED TO SERVICE.