Yep, use the Smart Battery case I got for 2015 Christmas and I had for my 6, ruined that phone
Then got a 6s last year and used that case until I lost it
And then I just bought the iPhone 7 and picked up the 6s battery case for $35 and love it
No need to pay $100 for the same case, but now I need to because of the red color!
I don't comprehend why someone would use any other battery case, this one you can see the exact percentage, it charges with your phone efficiently and it uses the damn Lightning connector, which other manufacters have a hard time doing, and you can save a life when you purchase!
Does the 6s battery case not cover your camera on the 7?