iOS 11: iPhone freezes/shuts down since update
There are lots of issues right now with iOS 11, especially with the iPhone 6S. A quick look at the iFixit Answers Forum will convince you of that. Of course, these are just a tiny percentage of all iPhone owners so it's not like there is a pandemic going on. If your screen has been replaced with an aftermarket screen in the past, this may be the source of the problem. 

This blog post explains:

The problem appears to be caused by the software driver of the Touch Controller IC that is embedded into the display assembly. Aftermarket screens produced with Hancai or Tianma LCD's using the Aichungjia (a Flex/IC manufacturer) "copy" driver appear to be incompatible with iOS 11. This driver is said to be unable to handle the iOS configuration and therefore shutting down and causing the lack of Touch functionality. OEM or Original grade iPhone 6S and iPhone 7 series replacement screens are not affected by this problem.

I don't believe it is battery related although you should check this Apple official website to see if you are elegible for a free battery replacement. Unfortunately, it is now too late to downgrade to iOS 10 as Apple have stopped signing those versions.