> I think people tend to exaggerate. If you say 9 hours, I'd believe 4.5 hours.
I'm describing tested battery life, not anecdotal estimations. E.g. http://www.notebookcheck.net/Review-Update-Dell-XPS-12-9Q33-....
Battery life obviously depends on your usage scenario, but the one described in the article is very light. Moreover, he's using a very low brightness setting, and seems to be using wi-fi intermittently. These points are important to note because on most workloads, the display and the wireless adapter are the major sources of power draw.
The usage described in the article is:
> I get about 6 hours of usage from a full charge (or more if I leave my desk for breaks and the screen shuts off after 5 minutes, which saves battery). As I mentioned earlier, that's usually on the lowest (or second to lowest) screen brightness setting, with the keyboard backlight enabled for about 50-75% of the time, and having Firefox open with 5-10 tabs, sometimes YouTube running in the background for some music, some Terminal windows open, Steam open in the background, Skype running in the background and a few text editor windows open.
Since idle background apps should take up very little battery, this seems even lighter than Anand's "Light Workload" scripted test, on which the MBA gets 11 hours (close to its rated 12). See: http://www.anandtech.com/show/7085/the-2013-macbook-air-revi.... Anand's test is at 200 nits (80% screen brightness). The author of this article says he's running at the lowest or second-lowest screen brightness, so maybe 10-20% or 30-60 nits. Even with the heavy workload test, which involves constant Wi-Fi activity and 1080p video playback, the MBA gets 5.5 hours.
If you mimic the usage in this article, with some apps open in the background, the brightness turned down, and typing into some terminal windows, the MBA would probably get 15+ hours: http://arstechnica.com/apple/2013/10/os-x-10-9/18/#battery-b....