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I have a 2010 13 MBA and have stayed with Snow Leopard for this reason. I've noticed many threads about lower battery life with Lion and ML, although supposedly better with 10.8.3. Using Coolbook, I can get over 10+ hours with my 2010. Great road warrior!
 
That's why I'm sticking it out with Snow Leopard in my late 2010 MBA. I think I'll keep it that way until I upgrade to a new model (I plan to do so in 2014).
 
Hmmm. I upgraded my 2010 1.86Ghz MBA just last month from L to ML and have noticed no degradation in battery life. Sorry OP. I'd say try escalating the issue to Applecare customer relations.
 
Sorry everyone..should have updated a while ago. I think I'm on 10.8.2 now, and I no longer have this issue. Not sure when it went away, but was definitely one of the updates.
 
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