Aura E2 HELP Kobo Aura Edition 2 Version 1 can't enter sleep mode without crashing

[Popo87]

Hi everyone !

Some week ago I posted here because I found a Kobo Aura at a garage sale, but it was completely bricked. With the SD backup image, I was able to get it working again, but it does some strange things.
Basically, the sleep mode doesn't work. When I put it to sleep, I can't get it back on after, and it crashes and reboots itself. It once crashed when I was reading too, rebooting by itself.

I tried to factory reset it, hard reset it, downgrade it on different versions of the firmware, but nothing does the trick.

It has a 8Gb SD card as the original SD wasn't in the reader when I bought it.

I don't know what to do anymore, is it possible that it's the battery ? What do I need to check on the PCB ?

Are there any crash logs on the Kobo that I could consult to see what happens every time ?

Thanks for reading, I hope to find a solution to my problem.