I'm looking for a device which can support a REPL for some reasonably pleasant programming language and has a very long battery life. I'd like to work on Project Euler problems with it.

If, for instance, an Alphasmart word processor could run a Scheme REPL and still run for 30+ hours on a set of batteries, I'd be delighted.

I own a PocketCHIP and can run the OCaml toplevel on it. This is very nice, but the battery life is only around five hours and the keyboard is not terribly usable.

https://en.wikipedia.org/wiki/AlphaSmart

https://hackaday.com/2018/04/03/is-this-the-end-for-the-c-h-i-p/

http://m5stack.com/