Wow, what a coincidence, I was reading a while ago that post.
And it makes me think that this could be the solution, a combination of sleep and power-off settings. If so, I'll think that the firmware developed by Kobo is quite poor.
Do not you think that there are too many complaints about the battery life of the different Kobo readers?
My KT has gone within hours from 38%, to the black screen message that warns low battery. No use in that interval.
And on this subject, does anybody remember which were the default energy settings? I'm now recharging and I want to test it with those values. The seller told me that there's no problem about replacing the unit, so I will make the test that Kobo customer service adviced me.
Have good readings!