We’ve seen 9 cell batteries for the MSI Wind before. Word on the street is that they’ll provide about 7.5 hours of battery life on a standard Wind U100 running Windows XP. I assume if you throw one in a newer MSI Wind U100 Plus with its more energy efficient CPU, you could eke out even more run time. But you know what I haven’t seen until now? A good benchmark showing how much battery life you can get out of a 9 cell battery with a Wind U100 running OS X.

Fortunately Wired Magazine’s Charlie Sorrel has come to the rescue. He picked up a 9 cell after realizing that using OS X causes his MSI Wind U100 battery to run down way faster than it would under Windows XP. As expected, the extender battery sticks out like a sore thumb. But while it’s not particularly attractive, it does tilt the computer a bit, providing what Sorrel says is a comfortable typing angle for the keyboard.

Most importantly, the battery is good for about 6 hours. A standard 3 cell battery dies after about 90 minutes if you’re using OS X.