The Quadro 135M is comparable to the 8400M if I remember correctly. The difference is the specialized drivers (CAD, 3d graphics work, etc.) for the Quadro. There are drivers out (forgot what website) that basically turn it into a regular Geforce
As for dual battery laptops, check out the Lenovo T61 but it has Quadro GPUs as well. HP might have a dual battery laptop as well but I haven't looked. What you are looking for is mostly in business oriented notebooks and a lot of the time have Quadro cards only