The battery use screen should/might tell you if something in particular is eating much of your power.
All Apps -> Settings -> About Kobo eReader -> Battery use
As far as I can tell, the information is about the period since the last charge. I took my Vox off of the charger to discover the exact sequence of clicks and notice that the screen only covers 1 minute. 60% Display, 40% Wi-Fi right now
Various parts of that screen are clickable for (slightly) more specific information.
Bitterbug: I'd be interested in what you discover (if anything) from that screen.
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