Aura H2O Battery drainage, interrupted sleep & segfault

[Torte]

I use a Kobo Aura H2O, tweaked with KBStartMenu_08, KoboRoot-AutoShelf-20151009, KoboTelnet, pbchess-2015.09_kobo.
The device consumes about 20% power each day.

I can't see a big drainage while reading, it seems to happen while being untouched.
The device doesn't stay in sleep mode, the "debug.log" from koreader shows, that it returns from sleep mode immediately:

[04/24/16 @ 16:29:28] Kobo Suspend: BEGIN!
[04/24/16 @ 16:29:28] Kobo Suspend: Current WakeUp count: 30161
[04/24/16 @ 16:29:28] Kobo Suspend: Asked the kernel to put subsystems to sleep
[04/24/16 @ 16:29:30] Kobo Suspend: Waited for 2s because of reasons...
[04/24/16 @ 16:29:30] Kobo Suspend: Synced FS
[04/24/16 @ 16:29:30] Kobo Suspend: Wrote WakeUp count: 30161 (0)
done_mem
[04/24/16 @ 16:29:31] Kobo Suspend: Asked to suspend to RAM... ZzZ ZzZ ZzZ? (0)
[04/24/16 @ 16:29:31] Kobo Suspend: END! (WakeUp count: 30166)

The "done_mem" line is from my addition to koreader's suspend.sh script, showing that the write is successful (it will fail with enabled usb-net):

-echo mem > /sys/power/state
+if echo mem > /sys/power/state ; then
+  echo done_mem
+else
+  echo fail_mem
+fi

It still shows the book cover in this (woken up) state, until koreader stops (see below).
I removed the sleepcover and left the device untouched, to not trigger any events, but that didn't change anything.
I also noticed, that after some minutes after the sleep, koreader always terminates, leaving a "crash.log" that contains only one line "Segmentation fault".


Has anyone an idea, how to find the source of a) the interrupted sleep b) the Segfault (without opening the device cover, as the device is quite new)?

Thanks,
Thorsten