As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EMERGENCY POWER LIGHT ON OVERHEAD ON, FOLLOWED QRH AND CALLED MAINTENANCE CONTROLL. CREW CYCLED ALL EMERGENCY POWER, OFF THEN ON, EMERGENCY POWER LIGHT REMAINED ON. RETURNED TO GATE. MAINTENANCE REPLACED EMERGENCY POWER SUPPLY. ALL CHECKS GOOD.