I think I got lucky and got one of the models with improved battery (Onyx Boox Page). I've been reading the Trigun manga on it for over a week now and it's only just getting to the point where I need to charge it finally.
But good point. Some of the older models might have worse battery life to consider. I only have a black and white model too. Color might use more battery.
Maybe look into an Onyx Boox instead of a Kindle. It will let you download books straight from the web (like standardebooks.org and Project Gutenberg) without having to side load. Also, you can add the Libby and Overdrive apps to it since it accesses the Google Play store. Also, it accepts all files formats so you don't have to convert anything.
Yeah, it's the price that bothers me the most about this. For the same amount, you can get a whole Switch Lite.
And I'm still salty about how they treated the Vita. This is what we get as the first handheld successor to the Vita? And the Vita didn't cost much more.
Wait, tyromancy is real?! I thought CDPR were joking when they made an entire quest line out of it in the Witcher 3. I got a nice sword called the Emmentaler out of it and everything. Huh. TIL indeed. Thanks, OP. I never thought to Google it.