gfxCardStatus Allows Easy Control of MacBook Pro Graphics Cards
Ars Technica has much more, including the fact that the Retina MacBook Pro can be pushed to nearly 10 hours of battery life with some minor battery saving techniques:
I was consistently able to get between 8 and 8.5 hours of continuous use from the Retina MacBook Pro when running integrated graphics only. Turning down screen brightness to just two "dots," a technique I often use to maximize battery life when using a MacBook Air during conferences, caused OS X to report potential battery life as high as 10 hours. I simply didn't have the stamina to test that claim, but I did make one nine-hour run with OS X reporting a nine percent remaining battery capacity.gfxCardStatus is a free download from creator Cody Krieger's website.