1999 Chevy Camaro Help car voltage low

My head lights want to turn off altenator, I though was the problem but today used the car and found that when I slam my brake to avoid hitting a dog my voltage on the gauge went back to normal and min later the gauge went back down to 8, it needs to read on the gauge 10 to 13, ok. I found possitlve battery cable eaten by battery acid could that be the problem and last is I have hid bulbs intalled, could it be a false contact or just the battery cable or should I change the altenator and battery cables by the way my battery cable is eateng up in one area only 30% is that enough to give me this electrical problem.