Got a bit of a problem..

I had summit UDP's on my car, with just a CAI..Battery meter kept dropping at night with the lites on, and when I'd hit the brakes it got even worse(abs light would pop on, lights really dim, radio shut off). It would only do that a little bit depending on how you were driving, as in how much you were on the brakes..or if you drove a long distance, and stopped and held the brakes in, it would not do it..

pretty sure I need to replace the alternator..

also took the alternator pulley from summit off and threw my stock one back on for a few weeks..didn't help..

what should I look for if I replace the alt, and it keeps doing this?