what size of alternator? are you doing the "big 3"? what batteries? there are a lot of variables. I have a kinetik 2400 with the big3, and a stock 130amp alternator, and im pulling around 2200wrms (2000@1ohm for subs plus a 4ch amp), and i stay right around 13+ volts, sometimes dropping closer to 12 at full volume and idle
do the big 3 and get at least an optima and you should be just dandy