I had my 6S battery replaced by a authorised repair shop. I don’t believe it was an official genuine Apple battery, but I dunno… anyway battery life was the same as before it was replaced, as far as I could tell. So, I swapped to a Samsung Android phone I had lying around and the battery life is phenomenally better, so I’m sticking with it. If Android wasn’t so messy with all it’s default notifications, alerts and the annoying way it remembers spelling mistakes and corrects the word you’ve just corrected back to the mispelled version(!!) I’d say I prefer it to the iPhone. 🙂