I am now pretty much exactly 5 hours into my random battery drain test: 50% battery left. I will note that about 1 hour of that was in sleep because I had to do some work away from my desk but, given what others have posted, that wouldn't matter much since, allegedly, sleep drains almost as much battery as when it's fully on (it doesn't). Including that hour of sleep, my projected total battery life for light use is 10 hours. If we exclude that hour of sleep where we'll assume that it did not use any battery at all (it used about 1-2%), projected total battery life after 4 hours of actual use is 8 hours.