I had a 6S+ and always had decent battery life: 10 to 13 hours of usage.
Updated to iOS 10 and the 6S+ battery life went south: down to 8 hours of usage.
Got a 7+ and initially I wasn't seeing any improvement over the 6S+ battery life.
Couple of things that worked for me. When I set up the 7+, I did it as new. I customized the background app refresh settings, leaving a few on, but most off. Still less than expected battery life. I went back in, and it seems that iOS 10 reverted back to all apps "on" in the background app refresh. (This seems to be a glitch as I have seen the same on my iPad: even though I customized the apps I wanted to use background app refresh, they all turned on again.)
Still less than expected battery life. I use Purify - so I turned off the background refresh for it, and also the stock weather app. Since doing that, the 7+ is now performing better than 6s+ was before going to iOS 10.
So long story short, check out your background app refresh. There may be an app or two in there to experiment with. Seems to have worked in my case.