Most eReaders use Linux. Kobo still provides software updates for models reaching all the way back to 2011. For something like an English novel Epub 3 is backwards compatible enough that it'll still work fine enough even on something like a Sony PRS-505 that only does Epub 2. And there's loads of tools like Calibre to back convert files if need be.

Really the battery is the only problem but some models do still have 3rd party replacements available.