Kobo Libra Colour Battery drain : my theory

Hi everyone ! I'm the happy owner of a Libra Colour but at first the battery seemed to be quite catastrophic, as reading for one hour or writing for as long would drain 10% right away.

But now I figured something through reading a book bought on Kobo : when I read this book (and highlight without the stylus) for an hour, i only lose 3% per hour ! Before that, I only read books from my google drive, which were epub formats.

So my theory is :

- kepub books don't drain the battery as much as epub (+the reading experience is more fluid)
- any use of the stylus is what drains the battery so much, whatever the use (reading+annotating or writing)

What are your thoughts on that ?

I was considering asking Kobo for a replacement but now that I noticed that, I guess my battery is not defective