I am wondering that too; I have a bunch of ESP32 chips that even have microSD card support, and that peak out at around 1W of power (I think). It's relatively easy to write an HTTP server for the ESP chips with Arduino or uLisp, and it's also relatively easy to get 10,000 mAh batteries; I wonder if I could get close to 99.9% uptime if I were to jury-rig something like that.
I also wonder which webstack would optimise best for power consumption. I suspect that something like nginx with lua and redis might be a good starting point, but that is only a very rough guess.
edit - thinking about it, I am a mile off. Will be something like compiling a custom server and having no OS.
