The Xʀ's battery life is insane. I had a 7+ on iOS 10 with a broken camera, reason for which I stopped using it after about a year, and I went back to my 6s on iOS 9. Even though I am not a heavy user, I always liked having the battery life of the 7+.
As a comparison, my 6s lasted 7-9 hours of usage, whilst the 7+ was at 10-13, depending on usage. So if I used them in the same way, the 7+ would end up lasting 3 more hours, give or take one hour at most.
I really missed that battery life, so when I got the Xʀ, I expected plus-like battery life, and it really delivered. It's even better than that. I had over 4 hours of screen on time and I had 80% remaining. That's slightly better than my 9.7 iPad Pro, when it was new, on iOS 9. I considered the iPad as the pinnacle of battery life, so to see a phone deliver more than that was mind-blowing.
I only got the Xʀ recently, so I couldn't test it extensively yet, but everything indicates it will be amazing. The best battery life ever on an iPhone, by far.