You might think this is a bit geeky but I have accurately timed the performance of my new Macbook Air 13.3 battery and here are the results, during the test wi-fi was on and screen was on one notch over half, time between sleeps varied from 1hr to overnight (8-9hrs), machine was not used constantly for these times, sat watching TV and surfing etc: Session One: Cold boot followed by general surfing of forums, shopping sites, ebay and news. Time 3hr06mins then put to sleep. Session Two: Wake from sleep followed by general surfing, 40mins on Google Earth, 10 mins on youtube, more general surfing. Time 2hr53mins then put to sleep. Session Three: Wake from sleep, downloaded plants vs zombies, approx 1hr playing PvZ followed by general surfing. Loaded 20 photos via SD reader and messed around with new slide shows in iPhoto 11 for approx 1hr. Time 4hr12mins then put to sleep. Session Four: General surfing, battery showed 11 mins remaining, plugged into power, end of test. Time 52mins. Total time for Battery from the above test 11hrs 3mins. I am mightily impressed with the performance of the battery on this thing, I never got anywhere near that amount of time on my 13" MBP's (2.26 and 2.4). I know there are all kinds of variables that can affect battery times but I am confident that this machine's battery outperforms any other I have owned for my usage.