What can I expect for battery life from my Nikon D5100?

You answered your own question. About 125-140 sounds right. The live view is your biggest drain, so the longer it’s on between shots, the less shots you’ll get.

I don’t use Live View, and have Image Review turned off, and I always carry a spare battery. I shoot all day and often have to change batteries, but never use up the second. Matt is right, if you want more battery life you may want to adjust your technique accordingly. Once you get used to the viewfinder you’ll rarely find a need for Live View.