2002 Ford Focus WILL NOT HOLD A CHARGE

THIS CAR HAS BEEN SITTING UNUSED FOR THREE MONTHS , i HAD ASSUMED THE BATTERY WAS DEAD . JUMPED THE BATTERY AND THE CAR STARTED . iT RAN ON IDLE FOR 15-20 MINUTES, THEN I DROVE IT ABOUT A CITY BLOCK AND IT CLUNKED AND DIED . i JUMPED IT AGAIN THE SAME THING HAPPENED . ONE MORE TIME AND I ROLLED INTO MY DRIVE WAY AND THERE IT IS . WHAT DO YOU THINK ? I AM NO MECHANIC , IS IT THE ALTERNATER.?

ONE MORE QUESTION , I DID NEW PADS ON THE FRONT BRAKES BUT THEY SOUND RUSTY AND SCRATCHY WHEN USED . WHAT DO YOU THINK IT IS.