Well, after charging some 12 hours, I managed to turn it on. What seems very strange is that the battery is at 27% (possibly because the screen was on the whole time, with white light at 18%, and the natural light at some 50%).
And just typing that, and checking the light levels, the battery dropped to 14%.
It seems strange to have such severe battery leaks on a new device (under 3 months old), and stranger that the screen remained on, which can only increase the problem.
EDIT: I remembered I already had a similar problem, at the beginning or November and posted about it:
https://www.mobileread.com/forums/sh...d.php?t=291913
I wonder whether I have a dud. My guarantee is until 1/09/2018, but it is annoying being abandoned in transit. I can read some on my phone, but it is uncomfortable and bad for my eyes in the long run - and I don't want to kill the phone's battery as well.