Perhaps you should consider the second internal battery then in a T4220? This will get you around 8 hours of battery life. Unlike any other tablet currently on the market, the extra battery doesn't expand the physical size of the computer, instead replacing the DVD drive (which you clearly don't need as you're comparing with the Lenovo). I would recommend against going with battery life that's only just what you need and no more; running batteries flat is very bad for them (as I have discovered; my battery is shot 18 months after I got the machine as I used to run the old T4210 for 7-8 hours straight of uni without a charge (on main battery only; you can actually do this if you turn all the power saving on and have the screen switch off when not in use. To be honest most people don't use their PC constantly all day; wish I'd got the secondary battery too now).