From a Which? article comparing Windows 7 and 8 battery life across various notebooks:
The worst battery life on Windows 7 came from the Dell Inspiron 17R, which managed just one hour and 45 minutes of web time.
How can Dell be satisfied shipping crap like this? In 2012?! That battery life figure is just web browsing time, let alone watching videos. I feel sorry for every single individual who owns one of these machines.
Say what you want about Apple, they would never ship something this bad.