Glo kobo glo frozen from sleep

I have a second kobo glo which exhibits the following problem, upon putting it to sleep with a sleep cover / case I got on eBay, next morning it does not come out of sleep.

The screen is frozen at the Sleeping / recent book cover screen. Seems to reboot when I plug it in the PC, I notice that the battery drops to 24%. running 3.3.0.

Thoughts?