Apple By Matthew Humphries Jul. 3, 2013 8:27 am

That battery life rating depends on what applications you are running, though. For example, movie playback will cut 2 hours off those times. What may surprise you is, using Dropbox seems to be by far the worst offender for killing your battery life. Leave it running in the background and your Air battery could be drained in just 3 hours.
This discovery was made by programmer and Qwikast founder Nico Schuele. He purchased a new 13-inch MacBook Air and proceeded to install his most used applications on it, one of which was Dropbox. After noticing he only had 3 hours of battery left after only 20 minutes of use on a full charge he started investigating what was going on.
The battery checked out fine using coconutBattery, and eventually Nico discovered Dropbox was using 90 percent of his CPU. File syncing was the cause, but even when that had finished Dropbox continued to draw quite a bit of power. Even with it paused he was only getting 7 hour battery life. It wasn’t until he turned Dropbox off completely that the Air reported 14 hours (using iStat).
So, if you own a MacBook Air or any laptop for that matter, it might be wise to disable Dropbox when you aren’t using it. As for Dropbox itself, it sounds like some work needs to be done to cut its processor usage in general, but especially when syncing files.
Now read: Mid-2013 MacBook Air: Hands-on Apple’s newest laptop