As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS IN BASE MAINTENANCE. PS CHECK EMERGENCY LIGHT TEST FAILED AND FLAGGED EMERGENCY POWER SUPPLY UNIT BATTERY AT 10WL. UNIT TEST SHOWED BATTERY FAULT, BATTERIES TESTED AROUND 5 VOLTS WITH MULTIMETER. REMOVED AND REPLACED THE 10WL EMERGENCY POWER SUPPLY UNIT BATTERY.