I'm not 100% sure about this but it might have something to do with your graphics card? I also have an HP Pavillion laptop and there I have options for my graphics card, i.e. the settings it will run if it's plugged/unplugged. Basically my system runs on a lower pace when it's using battery power while it switches to high settings once I plug it in. It could also be the case with yours (I'm not sure though because I'm not familiar with the model that you have)..