Did you buy both of the replacement batteries from the same place? If so, it is possible you just got two bad ones. I would try another battery from a different source, if you haven't already. There could be an issue where the phone doesn't like any replacement batteries, I have seen this a few times with various phones, but that is rare. Since it powers on with the old battery still, I would say it is most likely the case that you somehow just got two bad batteries.