[Apollyon202]

I’ve read somewhere that Kindles have both hardware and software power optimisations, while Kobo relies on software only.

I was using KOReader on my Libra 2, and the battery life was so bad I rather went back to Nickel instead. I'm not a fast reader, but still, even with Nickel one charge only lasts for 1 or 2 longer books and that's it.
Have to add that I always use the Libra somewhere between 20% and 85% battery charge.