Why I always have problem charging my Book?

Lately everytime my notebook is low on power I'll have to shut it down first before charging. If I'll plugged the adapter while I'm working it wont charged. Its not just the unit should have to be shut down I'll have to make sure that the cord and the unit is not touched becaused it wont charged or would stop charging. Really difficult to find a right position for it to charged. I have the adapter tested the result is fine. Now I suspected that the battery or the board itself or the power port has the problem.

I really need a very much helpful advice. Please.