battery life is not only factor of the laptop. having moved from Linux (ran gentoo quite minimal...) to freeBSD default install makes my laptop last about twice or thrice as long.

the art of idle software and efficient energy consumption is not landed in windows and Linux takes too much work..

mac does it not too bad + having good batteries, but thats not to say a laptop with a lesser battery should be trashed by a bad OS.

mobile operating systems are usually much more tuned to being good with battery life. I suppose Linux and perhaps windows do not seem to have laptops as main target even for 'desktop' distros or versions.