Why Won't A Brand New Alternator Not Charge A Battery?

Pull the pos strap off of the battery when the car is running, if it dies and you know that the alternator is good you could have a short. That could be what is killing your batteries.
 
Is your car killing batteries overnight? Could have a short somewhere else and that short just put more strain on your old alternator. Oh.. And I've been working on cars for 5 years and although I have very extensive experience with all sorts of cars I still make mistakes.  Ever see the issue of Hot Rod Magazine where they put an engine together and fire it up just to have it explode? They were mystified by what had made it do it until they took the engine apart and found out that they had left a ratchet inside of one of the cylinders! Everyone makes mistakes so don't assume that you did it perfectly.. And don't chew people out who are making suggestions.. You asked for the help!

We would say that if your alternator went bad, your car was running solely off the battery, which could ruin the battery.
Have the battery load tested.
Would be our bet that you need a new battery. Have seen this many times.
 Assuming that your new alternator is working.
♀  &  ♂

I would say it is the installers fault and that the alternator is probably working fine, but the alternator is either hooked up wrong or has a broke wiring harness or the belt is under driven or  this is the wrong alternator for your vehicle. or the best answer is you have a short somewhere causing the charge from the alternator to not reach the battery. In other words the pathway is broken. There can only be a few answers to this question. Something is broken/loose(wiring) /installed wrong/or the wrong part. Try the z net from autozone. It will give step by step instructions. You need to include further information of the vehicle(year/make/model/size engine/ if you want specific information.

Resistance in the wiring due to corrosion or poor ground. Sometimes theres a regulator that controls the voltage and amps within the alternator that is defective.

Have you had the battery checked to see if it didnt go bad when the alternator did or maybe the alternator was bad from the start an now its not charging .one way to see is to start car with nothing on in the car an remove hot lead from battery car should stay running if it do turn head lights on car should die

Grr ... If you been working on your own cars for 14 yrs then why don't you know? Instead of bashing people who are just trying to help a person who isn't smart enough to take the darn wires off and put in new ones cause there's a short .... Go back to your pile of junk and stop hating.