What was found
FIRST OFFICER WAS GETTING CLEARANCE. GOT INTO THE PLANE & REALIZED THAT THE VOLTAGE LOW CAS WAS ILLUMINATING. CHECKED THE VOLTS AND THE BATTERY WAS BELOW 24. SHUTDOWN THE AVIONICS AND TURNED THE BATTERY OFF FOR ABOUT 3/5 MINUTES. TURNED IT BACK ON AND THE CAS WAS STILL THERE AND THEN WHITE SMOKE CAME FROM THE CAS MESSAGE BAR. TURNED AROUND AND TOLD THE PASSENGER THAT WE HAVE TO DE BOARD AND FO WENT AND OPENED THE DOOR TO GET HER OFF. AFTER THAT, CONTACTED MOC AND DID ALL THE MX STEPS.