I bought my Asus laptop just for this. It has an advertised battery life of 11.5 hours, but I have never gotten that before. I can get 8-9 hours while actively trading with the screen brightness cranked down.
The SANDY BRIDGE ASUS CUSTOMIZED EZ LAPTOP will do this. The laptop comes with an SSD Drive and once all the trading stuff is loaded into memory the computer wont go back and forth to the drive