Battery Issue

Hi.

I bought a dell battery with serial "CN-07D1W-71802-8NX-06W7-A03". The battery charges fine and works ok but when the laptop is tapped, it goes off. The dell service center guys say the issue is with the battery. As, in it's not original. This doesn't make sense to me. The machine goes off even when it's on adapter when lightly tapped. What could be the potential issues?

Thanks.