Graphics card switching going haywire on battery

Just over the past couple of nights, my 'preferred' Intel graphics card for battery use will suddenly switch to the AMD card even though I'm not opening any apps that require it. I'm using gfxCardStatus and it will alert me to the change. I'm running the same apps on battery power that I was running three days ago, when my Intel GPU would be in use all of the time.

What could be up - I need one of you 'gurus' out there...

Clinton