What was found
AIRCRAFT WAS GROUNDED: MAINTENANCE REPORTS GATE CALL TO A/C FOR DARK A/C. UPON ARRIVAL FOUND EXT PWR NOT SELECTED, BAT 1/2 , ADIRUS SELECTED ON, EMERGENCY EXITS ARMED. SELECTED EMERGENCY LIGHTS TURNED ON AND NONE ILLUMINATED. SWITCHED ADIRUS OFF, EMER LIGHTS OFF, SELECTED EXT POWER ON. MAINTENANCE REMOVED AND REPLACED MAIN BATT 1 & 2 IAW AMM 24-38-51-400-001-A. OPS CHECK GOOD. ALSO PERFORMED OPERATIONAL TEST OF EMERGENCY POWER SUPPLY UNIT IAW AMM 33-51-38-400-002-A. OPS CHECK GOOD IAW SUBTASK 710-052-B. (SEE SDR # AALA201907159001)