Chevy Malibu /Connect the battery cables backwards.

What could be the problem be after ive replaced the
camshaft sensor, because my scanner insist on it even
after a new on. I replace the alternator eventhough it was
good come to find out. And a used computer(PCM) all
because it would start and run like always. (Great)
But after i put in the computer, which was the last
replacement it run great and after i did a security unlock
or refresh then it completely shut down and the battery
died within a matter of hours. The battery was dying also
though all of this real quick like right after i had it charged
so i bought a new battery. Almost forgot about that. I hope
someo e can solve this one for me.