My iPhone 6s suffers from unexpected shut downs. From what I can tell it happens when it is cold and when my battery has a good chunk of it expended. The last time this happened was yesterday when I was at the Reindeer Dog Parade in St. Joe. I had just under 70% left and my phone died. Once I got back to my car and plugged it in, it came right back.
Apple is aware of the problem and has a battery replacement program for limited batches of iPhones—ones made around September and October of last year. My phone qualifies for a replacement so I made an appointment with my local Genius Bar at the direction of Apple’s own website.
If you happen to have a qualifying iPhone 6s, go get that battery replacement but learn from my experience. Call the Apple Store and ask if they are going to be able to service your phone there at the time you go. It will save you a car trip. I made my appointment, drove forty minutes to Mishawaka (It was our first snow and you know how everyone freaks out), and checked in. The Genius looked over my phone, asked me a couple questions, checked the eligibility, had me sign a work order, and told me to come back in a couple of days. They didn’t have the replacements. Perhaps Apple could have saved us both some time and told me this before I drove all that way.