They're actually a re-brand of the Citizen PN48 portable printers... they do have a Ni-Cd battery pack in them, or run off the power supply you see in the picture.

There are a couple of ribbons available, single-use or "multi-strike". I'd bet this printer works fine with thermal paper and no ribbon as well. It's a good printer for the occasional printout, with decent resolution (360 DPI).