[Kraaz]

Like these photos, i choose galaxy S3 mini battery because of dimesions,
But i think your problem is, faulty power button switch, maybe resolder new one help. Or simple desolder old one, and solder 2 cables there on another switch glued on top of Kobo.

I marked area of power button , power switch is in other side of motherboard.

Changing Battery is not heavy task, i broked orijinal battery connector in motherboard, this is why i solder cables to motherboard , if you decide to change battery, simple cut cables on old one which have battery connector and solder these cables on new one , remember Red cable is always + one.
When you look at Kobo Glo motherboard, right side of connector pin is + .
So you need to solder cable on + side of new battery and - side of battery , then simple solder these cables with old connector from old battery. + side is red one in connector.