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: DURING EPSU SYSTEM TEST, EPSU (10WL) FWD L - DETECTED. REMOVED CEILING PANEL 221BC. REMOVED BATTERY (P/N#3214-31) OF EMERGENCY POWER SUPPLY UNIT (EPSU) 10WL IAW A321 AMM 33-51-38-000-002-A. INSTALLED BATTERY (P/N#3214-31) OF EMERGENCY POWER SUPPLY UNIT (EPSU) 10WL.