[Q] Battery Drain on Nexus 6 while using case topic

I have been using my Nexus 6 for around 2 weeks now - and have experienced good (as expected battery life running my usual config, using stock Lollypop.

3 days ago, I purchased a beautiful Stilgut Book cover case - since which I have noticed significantly more rapid battery drain consistently over those three days. i.e. Battery dies around 9pm rather than taking me into day 2.

I have come to the conclusion that since I havent changed any apps or my config, the case is having this effect - the book cover style flap auto sleeps/wakes the phone when opened or closed and I can only think that this is the reason for the battery drain.

Does this sound familiar to anyone (or anyone with similar experiences?).

Thanks.