What was found
ON PREFLIGHT, F/O FOUND LIGHT ON OVERHEAD ILLUMINATED, AUX BATTERY CHARGER FAULT NOTED. R & R MAIN AND AUX BATTERIES IAW AMM 24-31-11. R & R AUX BATTERY CHARGER IAW 24-31-31. PERFORMED BATTERY OPS CHECK IAW AMM 24-31-11, OPS CHECKED GOOD. PERFORMED AUX BATTERY CHARGER IAW AMM 24-31-31, OPS CHECKED GOOD. CLEARED LIGHT ON OVERHEAD, LIGHT REMAINS EXTINGUISHED. FOUND GROUND STUD GD3308-DC LOOSE. SECURED GROUND STUD. MAIN AND AUX BATTERY CHARGERS GROUND VERIFICATION TEST PASSED REF MM 24-31-31 AND 24-31-21.