One odd thing is that my iPhone 7+ has battery issues and the battery is new. My iPad doesn't have battery issues. My belief is that there's a voice/text issue with the phone spending more power trying to talk to the tower. I am running the phone on Low Power mode and that gets my battery life back to being decent. But I shouldn't need to have to do that.
I have a 7+ as well, which I set up as new under iOS 13.1, and I too am seeing worse battery life. One thing I’ve noticed is that the battery usage indicator has twice shown apps running constantly in the background that didn’t stop until said app was uninstalled. In one of the cases the app was only allowed to use location while the app was running and background refresh was disabled. That didn’t stop the app (Yelp) from running constantly for 9 hours straight until I uninstalled it.