So once "the end" comes, you'll be set for a good 4 hours before your phone runs out of battery?

You could recharge your phone using sticks (https://www.rei.com/product/115523/biolite-wood-burning-camp...) or a solar panel.

I wonder what the longevity of something like that is. And for solar panels what do you do if it's a supervolcano that blocks out the sun? The real solution is a radioisotope thermoelectric generator which will give you a few hundred watts for decades. But I don't think they sell those online...

My phone lasts a good 20 hours!

Also, I do have a solar cell, but yeah, modern phones aren't really designed for post apocalyptic conditions surprisingly.

Fortunately, all that is also useful in tunnels, underground bars, the countryside and when travelling abroad.

For what it's worth, I have an old cheap LG phone that I once accidentally sent through the laundry and it was fine.

By offline Wikipedia dump, you mean Kiwix?

(https://www.kiwix.org/)

Well Kiwix is the reader software rather than the dump. I use a huge dump that includes images, but there are lots of choices inluding other reference works and in other languages (useful for learning). I've used a number of different offline readers over the years, TomeRaider, Aard, but kiwix is the one I use at the moment.

Wait, is there anybody else other than the guys behind Kiwix who regularly make compact archives of Wikipedia? The only place I know of where you can download a premade archive (rather than archive it yourself) is off their servers.

I don't know about regular, but there are lots of dumps out there, and you can make them yourself if you have your own preferred format. Lots more information here:

https://en.wikipedia.org/wiki/Wikipedia:Database_download