Yes. At least, I think so. It might also be very long chapters, or missing chapter marks. Are you reading kepub (directly from kobo) or epub (sideloaded)?
Kepub will load one whole chapter into its cache. So the bigger the chapter, the quicker the battery life will drain. I'm not sure how epubs are loaded, but same book gives less dramatic results, but still not long enough battery life.
I have a thread about my experience here
https://www.mobileread.com/forums/sho...d.php?t=201790
You could try splitting the the bundle into the actual 6 books. Calibre has a plugin called "EpubSplit" which works extremely well. I've used it a couple of times on every bundle I bought.