Interesting. My PN40 is officially only speced for 19V, but I run it on 12V all the time, without issues. After all there's nothing within such a computer that runs on 19V - that (most of the time) is only to guarantee a stable 12V when converted down. So I'd just try it with 12V. You might just need a strong enough PSU or large enough battery that doesn't drop below 12V, as an i7 might well need some power...