The Onyx web page claims " a month of autonomous working period" does it mean with WiFi off perhaps? Does anybody know?
I own a Max 2, but I guess that my answer fits the Note as well.
For sure this is the consumption in the best possible scenario, that means wifi turned off and using the device as an ebook reader. In my case, the wifi drains the battery very quickly, thus I turn it on just when is needed.
I use the Max mostly for reading and writing in offline mode, and when I have finished I run dropbox with wifi enabled in order to sync my laptop.
If I keep the wifi off and let the device in standby when not used, for sure the battery charge is enough for a couple of weeks.
it’s probably rated for a month just like the e-ink kindles, wifi off and only X minutes of use per day
in other words, it’s like car MPG ratings, no connection with the real world 
I will say that I can go through multiple books with the wifi off with no problem, that’s good enough for me.