3 - 4 years has gone to durate of the battery of your onyx boox max, i have it since 2016 and already i have gonne problems relate with the battery, its duration is of 4 days, in effect, what you dont go to own this much of the date mostrate up, i think that the price its too much expensive for the life of the product, besides i think that onyx dont is much friend of the program obsolescence, by dont mention of the culture and the igualate of oportunities.
perhaps you’ll agree with me that battery life depends on how you use the device and what applications you have installed on it. The possibility to install applications on Onyx devices via Google play is a great advantage, but this unfortunately has a great influence on battery performance. We can’t always blame Onyx.
As a comparison… my phone batteries are usually noticeably degraded after 2 years, needing replacement after 3.
I don’t think 4 days between charges is too bad for a 4 year old device.
Considering I use my e-reader for hours every day, I don’t mind replacing it every few years.
Even if yours have a quite part of reason, 850 € every 3-4 years seems me an abuse.