I have consistently had the backlight on 40% and just casual web surfing and email checking, and I have noticed that the predicted battery life on my unit (SP2 8gb model) has been quite inconsistent. I've had reports of 2 hours remaining on an 86% charge all the way up to 10 hours. I was wondering what I can expect out of this device. I also own a non haswell MacBook pro and I get about 5-7 hours out of that. Can I expect about the same from this?