Does your iPhone 6 suddenly shut down for no apparent reason?
This issue is coming from a bug that appeared after upgrading to iOS 10.
Both the iPhone 6 and the 6S have been hit but only the latter is subject to the official battery replacement program from Apple.
As a runner, I’ve experienced this problem and the colder outside, the faster the iPhone would shut down unexpectedly, starting at around 50% charge.
Then, to get it back on again, it could take between a few minutes to sometimes 10 minutes (which I suspect is linked to the charge level and the temperature of the battery).