GreetingsCustomer

There are a few things that can cause this...You need to check the battery cables for a good,clean connection and tightness...also you need to check the wiring at the alternator for good connection and also that the alternator ground is good...any of these will cause a low or no charge condition...also check for voltage drop in the battery cables ...Finally,test the alternator at the battery with the car running...should be 13.5-14.5 with engine running....if not the replacement alternator may be faulty or you may have a faulty connection or component in the circuit itself...It may also pay to check for a parasitic draw on the system if the battery goes dead overnight...your description sounds like you may have 2 seperate problems,so do each test one at a time until you locate the problem...jeffrey590