I have a dual boot Chuwi Hi8 Pro, and it still has the same battery issues. It shut down at 36 % reported battery. I let it charge over night, but the charge stopped at 77 %. It also reports a 8000 mWh battery, which is probably the source for all the confusion.
It still works, though ! I just try to keep the battery charge as high as I can to avoid the < 40 % charge sudden death. It takes hours to even charge a few percent, though, even when the tablet is switched off.
Pretty crappy if you ask me. Much happier with my Teclast X 98
