Problems with alternator? in 2006 impreza 2.0

[eriknoi05]

so i bought a 2006 Impreza a couple of weeks ago and after 2 days of owning it the alternator stopped charging i was getting maybe 12volt charge with the engine running on the voltage meter and the battery was slowly draining. but every direction was pointing to the alternator so i swapped the alternator easy peasy and it read 14.60v and it worked fine for a week, until the battery was dead again so jumped the car and when i took the cables off the car the voltage meter was reading 8v and then it quickly died. so i charged the battery and turned it on and it was reading 12v on the volt meter. i tried taking the battery of my Yaris and put it in the Subaru and it also read 12v. so i dont think the battery is the problem could it be the new alternator is faulty or is there some sort of connetion issue? (btw the battery light never came on which is strange) thanks in advance.