Does the 2011 13" MacBook Air have a longer battery life than the old one?
Actually, the previous MacBook Air 13" (2010) used a Core 2 Duo SL9400 or SL9600 which both have a TDP of 17W.
The new MacBook Air 13" (2011) uses an i5-2557M or i7-2677M which both have a TDP of 17W too.
I don't think we can say that these new CPU consume less power.
- MacBook Air specifications on Wikipedia
- MacBook Air 2010 CPUs on Wikipedia
- MacBook Air 2011 i5 CPU on Wikipedia
- MacBook Air 2011 i7 CPU on Wikipedia
My personnal opinion is that Apple tried to stick to the power consumption while boosting the performance by switching to a more modern architecture. I do not expect Apple engineers to work on switching architecture AND improving power consumption at the same time.
So to answer your question:
No, I would not expect a longer battery life with these new CPUs. Even a little reduction for those with an 11" MacBook Air because their CPU switched from 10W to 17W.
Apple hasn't changed the claims about battery life. 7 hours for the 13,3", 5 for the 11,6". It's a bit strange that according to Apple the batter life didn't change. Maybe we'll get a nice surprise.
Found it here: http://www.macrumors.com/2010/10/20/apple-announces-new-13-3-inch-and-11-6-inch-macbook-air-models-with-flash-storage/