Losing Power

My iPhone is acting up. I have it on the charger and it is losing power. The battery says that it is ok so what is wrong? I have been walking around the house plugging it into different rooms as I go. This happened a few months ago and I took it to the Apple store. They said it was fine, played around with it and things were great until now. I will try playing with it today and maybe it will snap back into shape.