As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN EMERGENCY EXIT LIGHTS ON WITH NO AC POWER ON 3 MID CABIN LIGHTS EXTINGUISHED AND 1 OVERWING AC-R EXTINGUISHED 20 SEC AFTER INITIAL ILLUMINATION. GROUNDED - YES. REMOVED AND INSTALLED SERVICEABLE POWER SUPPLY & BATTERY PACK ASSY OPS CHECK GOOD IAW B737-900 AMM 33-51-06-860-806.