Don't update to iOS 11 in any device.
I have an IPP 9.7 (128 GB wifi only) that wasn't used and most of the time I kept in the drawer. Then I installed the TSTAND in it:
https://goo.gl/64gMJp
(And since then it wasn't removed, because it's easier to leave it that way, removing would wear the stand and require two people). Also had to stop using the Smart Cover, then for some time I only used auto-lock for 15 minutes, later 10 and now 5.
And since then I started watching videos and using it as my single device, after my other IPP 9.7 was sold. Even this IPP 9.7 (256 GB Wifi+Cel) didn't have a 10% degradation in the battery. And I am sure it was used a lot.
In two months the degradation of the battery (from the IPP 9.7 128 GB) increased from 6, 7% to 10, 11. That alone would be acceptable, if for the first time during the day I didn't have to recharge the IPP 9.7 because the battery dropped to almost 0.
I don't remember having to do that since I had an iPAD 4, and when I sold this iPAD 4 it had almost a 30% degradation. And I don't believe at all that even by watching videos during the day and with 50% brightness the battery could be used so fast.
I would be deeply surprised if iOS 11 haven't done something wrong with all the batteries out there, and of course this can only benefit Apple, that forces you to replace your battery or the device, so this must be on purpose and is far from being a conspiracy theory.
My IPP 10.5 won't stop using iOS 10.3.2 and I plan to cease updating apps too, if they are going to become broken in it. I want my equipment to last as much as possible, and replacing any used battery (at least for iPAD) is either costly or can't be done.