I and my wife had exactly the same issue today. We both have iPhone 6s Plus. We went for a walk today afternoon and it was about 6°C outside (it started getting cold, as winter is coming). My phone had about 45% battery and phone of my wife had about 60% battery, and after 10 minutes of walking both phones almost simultaneously turned off without any notice! 😟😟😟 We tried to turn them on, then it was said that we shall plug it in to recharge (completely nonsense). After second try, by holding the power button, and finally my phone started and then turned off again after about 40 seconds of start up and using it. The similar situation was with the phone of my wife. We rapidly tried to turn on the phones so many times, but it was unsuccessful and the same each time.
The most interesting part of this story was when we came back from outside and in a few minutes both phones turned on without any difficulties, and my phone had about 30% battery!!! and phone of my wife had 40% battery!!!
Both iPhone 6s Plus are less than 1 year old. It's obvious that not only iPhone 6s has hardware issues with battery in cold weather (as Apple reported), but also iPhone 6s Plus.
I use iPhones since 2007, every year I was changing the model and since that time I never had any issues with battery, even when outside temperature was below 0°C, with all my iPhones I had in the past.
I am very disappointed on that kind of quality of hardware which costs ca. EUR 1100!!! And what I really don't like that winter season is coming and I might face this issue every day and so many times per day that I can even not imagine!!!
@Apple, please try to solve the issue and not hide it. Customers will thank you for that, otherwise you loose them by ignoring this hardware issue. The story with Samsung Note 7 is a good reference to think about.
P.S. As my warranty is still valid, I am going to file a claim and will see what is gonna happen.