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There are a combination of reasons. Chrome OS is a lightweight OS, and I assume that is it somewhat more efficient at power management than Windows. Note that MacBooks tend to also have better battery life than Windows laptops, although part of this may also be better quality batteries and tighter integration of hardware and software, as well as more efficient power management by OS X . A major factor is the lack of HDDs in Chromebooks. A HDD takes a lot more power than a SSD does. Chromebooks are about to get even battery life with the new Nvidia Tegra processor, which is very power efficient and the first Chromebooks that make use of it are showing 12+ hour battery life. As hardware developers put the lessons learned in the mobile market to use in laptop (the Tegra K1 has its roots in mobile devices) I think it will get even better.