I am looking for a very small, lightweight computer with a full-size keyboard for taking text notes. Ideally it would be 500g or less including batteries for 16 hours of use. And writing text is the only use - a typewriter, if I could find one light enough, would be just fine.

[I realize this is not the place for product recommendations, and that's not what I'm looking for. Rather, I have no experience in this space, so what I'd like is to understand what kinds of equipment are available and what are the right keywords to plug into Google/eBay/etc. In other words, help me learn enough to do a worthwhile search.]