The above comment about "devices dying, electricity going out" ...
... is a good segue into what can be easily done about these issues. Note that it *is a good thing* to both have a physical copy and electronic copy (ebook, pdf, etc.) of something that is worthy of sticking in your library. In my case, the kindle just makes it so easy to pull out and have the reference at my fingertips, while in the field (this is daylight readable, like a book).
To *avoid* the issues of devices dying, and electricity going out, is very easy. As suggested in plenty of other threads, have multiple layers of security (devices), and multiple backups, and even backups of backups. It isn't really all that technical ... although it may sound like it.
If you have a kindle, there is no "electricity is down, can't power up my computer, therefore can't read a book", as the kindle is a standalone device. The daylight readable aspect makes this the perfect vehicle for reading a book, at any time, at any place. If I drop my paper book in the toilet, while reading it (not that that ever happens to me), it's toast. If I drop my kindle in there, it's also toast, but not a total loss, because it is super easy to have my *entire* kindle library on my pc. With a new kindle, or a dried out one, I just reload the entire library.
Same thing on a phone ... get one with an SD card slot, and keep a copy of the entire library on there. Plug it in, and instant library at your (phone) fingertips. If the computer dies (not that that ever happens to me), just reload my valuable library from the SD card (or computer backup ... right?)
But wait, who wants to fiddle with all those file extensions and acronyms, like .pdf, .epub, .whatever ... not me! Which is why I always recommend open source and free software for everything (very doable), and in this specific case ... CALIBRE! (yes, I was shouting ... it's that good of a *free* product). This software package will let you stick in any electronic copy of a book that you might have, buy, or otherwise come across (and there are more free books out there than I can shake a ... stick ... at). Then, the magic occurs ... it lets you push a button and transform that book into any other format, for any other device. No longer are you held captive to some device or format. No extension madness ...
Again, have your cake, and eat it too! Always get the paper version of a book (if you can, as some are out of print or wayyy expensive), and an electronic version! Oh, and get a kindle or similar to read it anywhere, anytime.
Just not on the toilet ... not that I've ever done that.
BTW, I'd put this in the computer forum, but it seems to have not been created yet (that I can see)?
https://permies.com/t/165030/Computers-Forum