My Onyx Boox Max Lumi certainly has excellent battery for my purposes.

Also owner of a ReMarkable 2, will be reviewing both of them soon as I think they are an interesting niche tech, and are big investments for people.

Hard to say because I have auto sync set up to keep my PDFs up to date which runs every 15mins. And Wifi is mostly on. But with that and moderte usage I may need to charge it between 7 and 9 days. But you can probably do optimize the settings more (after what time does it disable wifi when it started sleep mode, when does it start to shit itself off, front-light adjustments, etc.)