I’ve been struggling with the fact that my iPad Mini 6’s battery will drain to zero in just a few days, even if I’m not doing anything with it. My iPad typically lives in my bag, and it’s happened more than once where I’ll charge it up, and a few days pass before I go to do something with it - and it’s dead.
The important preface to the rest of this post is that I don’t regularly use this for my email, calendar, etc. - I use it for taking notes, e-reading, etc. I don’t need it to be doing all the “extras” - I just need it to light up when I press the “wake” button, and be able to take a note, show me an ebook, etc.
And an important part of the spec for getting this to work was that I don’t want to have to remember to turn it off, and I don’t want to have to wait to power it on. I need to be able to take it out of my bag and do my thing.
I’ve tried lots of things, and while researching I eventually landed on this article:
I did all of that (automating “low power mode” below 95%), and also disabled the smart cover wake as I’ve seen things about it getting jostled in a bag and the screen waking up. Also made sure to store it without the Pencil on it, obviously. 
I decided to see how long it would go without any use.
I didn’t officially keep track of an exact “start”, but according to my iPad, the last time it was fully charged was this last Friday (6 days ago), and all I’ve done every morning/evening is flip open the smart cover, press the unlock button, and swipe down to see the battery percentage.
This morning it’s at 51% battery. So I’ve doubled my previous “best” of about 3 days, and it still has enough battery left to be useful. I probably could have taken notes / done some e-reading throughout the week and I’d just be getting close to needing to charge it.
I realize that disabling all that stuff impacts other things you may be doing, so this isn’t for everybody. But if there’s anybody with a more occasional use case, I figure this might be helpful.