As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: OPERATIONAL CHECK OF EMERGENCY LIGHTS FAILED DURING ACCOMPLISHMENT OF PS CHECK. FAULTS READ "EPSU BATTERY EMER L" AND "EPSU INT LOAD EMER L". REMOVED AND REPLACED EMERGENCY POWER SUPPLY UNIT BATTERY PER AMM 33-51-38.