Yes all companies love to state their maximum battery life and you won't get that battery life. To get the stated battery life you would have to run basically nothing, dim down the screen, lower the CPU/GPU speeds, cut off wifi, be in a fairly cool environment, etc. If a company states that their battery can last up to 9.75 hours you really won't get that. Obviously if you do "heavy" things with your computer you will drain the battery life a lot quicker.
With my tests I have figured out that my X220T 6-cell with "average" usage can give me about 5 hours of battery life. Those five hours mean that I can browse the web with a few tabs, watch some Youtube and Hulu and so on. If you do push the system you will get about 1 hour. Lenovo does have that battery slice so you can pretty much double your battery life. The battery in the X220T has improved from the X201T which gave me about 3 hours and 20 minutes with an 8-cell.
HP states that their 9-cell will give about 9.75 hours and that is also BS. I get between 5 and 6 hours with Intel HD graphics on. I have not tried any tests with the discrete graphics but I wouldn't be surprised if I get less than 3 hours.