What was found
TRIED TO START THE APU TWICE, NO START. APU FAULT EICAS. OPENED PANEL ON THE E-6 RACK AND NOTICED APU BATTERY COMPARTMENT WAS FULL OF SMOKE AND SMELLED STRONG. CHECKED APU AUX CONT UNIT, NO FAULTS INDICATED. R AND R THE APU BATTERY IAW 24-31-04-4. OPS CHECKED GOOD, APU STARTED AND NO SHUTDOWN, EICAS FAULT CLEARED. ACFT OK FOR SERVICE.