Another solution is https://www.packedpixels.com/ but the size is not so great.
I currently carry a Sharp LL-S201A which is slightly larger than the above ones -- I got a great deal off eBay for once. If I didn't then probably I'd get one of the 17" ones above -- the Sharp needs a VESA mount which makes things unwieldly.
Besides that, the quality and the feel of the device is pretty nice.
I bought it because I figured it'd be a decent netbook to break out when there's a network issue or that I could use it for IRC or programming while traveling. Instead it's just collecting dust.
[1] https://github.com/ayufan-pine64 [2] https://forum.pine64.org/showthread.php?tid=4729
And yeah, it's mainly Ayufan busting his butt with all of the pinebook distros, with a little help from two or three others. But he's pretty much hammered out all the issues that Ubuntu had upon the pinebook's initial release, and he's active on the Pine64 IRC if you ever run into any issues.
I run xenial ubuntu with i3wm, and it's fine for on-the-go programming. I've been using it to learn Common Lisp at coffee shops. Don't bother if you're a React/Angular/Vue etc developer; the build tools will take too long for it to be productive. I'm not even sure if it can handle ruby sass, for scss scripts.
So yeah, it's great if you want to tinker with a cheap ARM notebook. But not great as a daily driver, or any complicated dev work.
And frankly the rest of the laptop is not very complicated.
[1] https://hackaday.com/2017/04/28/hands-on-with-the-pinebook/
people get very annoyed when they know what that really means. Say for example, every power bank available says 10,000 mAh, or 20,000 mAh (or whatever), but all those are at 3.6 volts (not at 5 volts). As most of the other specs is in 5 volts, most people don't even know this.
Neither amp-hours nor watts measure energy. Watts measure power, which is irrelevant for a laptop battery, and amp-hours measure nothing unless you know the battery voltage.
The spec for a battery should be in joules or watt-hours.
With the largest battery I could find for it, it easily got at least 10 hours, IIRC. I don't believe it approached 20 hours, but this was also about 7-8 years ago.
I don't remember the exact model (it was one of the later ones they made, I believe). I have it around here somewhere if you really want to know which one it was.
The worst part about it was the screen resolution. It was something like 1024x600. There were a few applications and light games that assumed your screen was at least 768 pixels tall (Photoshop CS2, for example, which otherwise worked perfectly in WINE).
For something a bit more modern, I'm continually intrigued by the GPD Pocket Mini Laptop [1].
[1] https://www.gearbest.com/tablet-pcs/pp_613003.html?lkid=1106...
A Chromebook might be able to do what you require for 9-10 hours, with a little tweaking.
Probably wont hit 20 hours, but I could imagine 12-14, which is pretty respectable.
If anyone has definitively solved this problem, I would love to hear about it. I've dropped 50+ USD on apps trying to make this happen.