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My understanding is that the new MacBook Air 2011 is using a new Intel CPU that uses less power. I expected that should mean either longer battery life or a lighter computer, but I can't remember how much battery life they claimed the old one had...

Should I expect longer battery life from the new MacBook Air 2011?

To simply ask your question; the answer is "yes" if you do simple everyday tasks such as internet usage (web surfing, email, streaming videos) or development work (with 1 VM running in the background).  The answer is "no" if you do gaming on it.  But if you want to do serious gaming on it everyday, don't get the Air.
For a more detailed analysis, read below:
note: I don't own a 13", but an 11"; however Apple's battery claims for the 11" are 9 hours (a whole 4-5 hours more than the previous year's model).  So take all my values and probably add it by 3-4 hours for the 13" model.  Also, I have the upgraded i7 CPU model, which is supposed to use up more battery than the energy friendly i5 base CPU model.
For normal day-to-day tasks, such as web browsing, watching youtube, email, etc:

  • To really put it to the test, I set the brightness at around the 3 bar setting (which was optimal for me at night), it said I had about 11-12 hours of battery.  This was the absolute minimum I can set the brightness such that it was comfortable enough for me to read.
  • I set the brightness to 12 bars during the day and that's more than enough for me (even half or 8 bars will do too sometimes), and I usually get about 6-7 hours of battery.
  • Just for fun, I set the brightness all the way to max (16 bars) and battery drops down to about 5 hours.
  • I read an article on Review Apple MacBook Air 11 inch Mid 2013 1.7 GHz 256 GB Subnotebook that said leaving the macbook at 1 bar resulted in the battery lasting 23 hours and just using the screen for reading, no internet usage; internet usage resulted in 13 hours.  (Scroll down to "Battery Runtime")  But in my opinion, the 1 bar setting is uncomfortable to read (apparently, it is equivalent to candle light); but that's just me.

I tried putting it to the test with a 3D game that would put the CPU at 100% usage, and my battery life plummeted (unsurprisingly) to 2-3 hours.
For my everyday usage, I'm always either at home or at the office when I have my MacBook; and therefore, it's almost always plugged in.  The few times that I've had it on battery, it's been great so far; I haven't had a need to carry around a power adapter yet, and I don't worry about it running out of battery for an entire day at all, even for the 11" model.  I imagine the 13" model has a far longer battery life.
Hope this helps.

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A 2011 MBA’s two big battery drainers are the LCD backlight and the CPU though in testing I did find that turning off BlueTooth and WiFi bought me about a half hour more battery time. When new my MBA gave me between 5.5 and 6.5 hours of real use. It is now 3.5 years old and I have 300+ cycles on the battery. I am getting between 4 and 5 hours on a charge. By real use I mean I’m not turning the backlight down until I have to squint, I’m using my programs as usual, and I have WiFi on. I keep BT off normally.

If you are getting 3 hours in normal usage on a 2011 and that isn’t enough, you should consider getting it replaced. The cost is $129 in the US and can usually be done at an Apple store while you wait. (Call ahead to be sure.)

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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.

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.

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