Check out the POWERPAD at electrovaya.com. It powers thru the AC Port, and the high VA model will probably run your unit all night. They're a little pricey, but for the size and footprint, they can't be beat.
Check the Model Compatibility Guide to make sure your computer is supported.
Shame my Sony GRT-100 uses a 19.5V input, and I can find ANYTHING REASONABLE (in size, $$ is no object) to power it in the field. I "over-spec'd" on power/screen size, before I checked whether I could power the damn thing remotely.
Rick