To clarify, does the battery show as charging when plugged in? If so, will it go from no/low charge back up to half charge? If this is the case, I would contact whoever sold you the battery and ask for a replacement.
I had a similar problem when pressing on the center button. Turns out it was too much solder on the battery connector. I had to disassemble again and used some solder wick to lower the solder blobs. I suspect that the back plate must not be completely flat for you.