1999 Dodge Intrepid replacing alternator

Yea I figured I would have to move the fan assembly already done installed salvaged alternator dang battery light came on again after all that work. So I took old alternator that I originally pulled out back to oriellys since they are the ones who said it was bad and had them retest it now that it was out of the car and guess what? Its good. Is it possible that the battery wire not making good enough contact so that when car is running its drawing all the juice from alternator and the reason im saying this is a week prior to battery light coming on dash my battery went bad and I went to walmart had them put new one in which wasn't easy because in wheel well.A week later have light on dash come on showing battery drove to oriellys they test where cables are at for jumping car say that low output from alternator I barley made it home battery was almost completely dead so made sense to replace alternator. But as I said alternator is good so any idea I really would appreciate it sincerely Thomas hathcox