Update 3: I charged my Boox on Monday, around midnight, so it should be fully charged by Tuesday morning. Today is Friday and my Boox only has 1 bar left. Admittedly, I haven't done much reading. I remove the SDcard often, experimenting with different formats, so I open and close many books many times too. That probably use more battery rather than just reading one book at a time. I probably have to recharge it tonight.
I also found something interesting: Boox can read ebooks from zipped files, but it treats it as a different format than what is contained inside. For example, I converted an ebook to epub with Calibre and it resulted in 1 epub file, 1 jpg, and 1 opf, I zipped all those, and when I opened it with Boox, it treats the ebook more like an html file. The menu is different from what you'd get if you open an unzipped epub.
I only get roughly 4-5 days with the way I use boox so far. I also never turn my Boox off, only stand-by. After my next recharge, I'll try to turn it off every night or use the auto turn off feature and see if I can get a longer usage time / charge.
So my next suggestion is if Boox can add an auto turn on/off based on time. Say, I want my boox to automatically shut down every midnight and turn on automatically every morning at 7 o clock. I wonder if that is possible
Edit: My boox just completely ran out of battery lol