Check both ends of the battery cables (that's 4 total ends) for corrosion. Charge the battery and see what happens. Have the battery load tested just to make sure. Where did you buy the alt. Chances are it is the alt. I went thru 5 of them until I got one that lasted more than a week. The last one tested good at Autozone but I had them refund it and went to O'reilly. It took 2 there.