My 2000 maxima is charging at 14.1v when all accessories are off and drops to under 12.5v when accessories are on. Recently replaced Alternator that was under warranty. Noticed that car was charging at a little over 11v so I cleaned the bat posts and terminals. Could this be a bad regulator in the recently replaced alt?

 

have you checked your grounds? maybe the cable from the alternator to the chassis is bad? Also as an example maybe something is running, let say the window even when they are closed and you push the button it still uses power and drops the voltage a bit. Could be stuck