Apple says iOS 10.2.1 has reduced unexpected iPhone 6s shutdown issues by 80%
If, like me, you’re in the unlucky 20% who find the upgrade to iOS 10.2.1 doesn’t really help., this just means your phone will randomly die less often. The two things that tend to lead to random iPhone deaths are cold weather and listening to Apple Music.
The real solution? Carry along a spare battery back. I’d recommend the Omaker portable charger, but they don’t seem to be available any more.