Battery Problem. I purchase a Battery off the net, and tried to use it on my psp, a Sony PSP

Question

I purchase a Battery off the net, and tried to use it on my psp, a Sony PSP Battery Pack 3.6v 1200 mAH converted to a Pandora Battery. What the problem is, is that it won't sit properly in the PSP so I can charge or use to reset my system. The original battery is a Sony PSP 3.6 1800 mAH, which is slightly thicker than the one I bought and works fine, sits quiet neatly in the player. I have had the orange light come on likes its charging the Pandora but then it flicks off if I move the PSP. I not sure if it could be the battery contacts causing the the problem. Any assistants here will be much appreciated.