What was found
WHILE ON APU POWER, DURING ENGINE START, ELECTRIC LIGHT ILLUMINATED. ACFT GROUNDED. PERFORMED FIM 24-31 TASK 801, AUX BATTERY CHARGER FAULTED. PERFORMED FIM 24-31 TASK 835, REPLACED AUX BATTERY CHARGER IAW AMM 24-31-31. REPLACED AUX BATTERY IAW AMM 24-31-11. RAN ENGINES TRANSFERRED POWER BETWEEN SOURCES, NO FAULTS NOTE.