Charging battery and high CPU usage - Help!

I just picked up a new notebook and am having a weird problem with high CPU usage.

When I run on battery power there is no problem. CPU usage is fine and I can use applications as I would expect.

As soon as I plug in the AC charger the CPU usage jumps up to 20-40% and if I open IE it jumps to 90-100%. It takes more than 30 seconds for a window to open. Using any application is incredibly sluggish. If I unplug the charger the problem goes away immediately.