IOS release 10.2 worsened the problem with spontaneous disabling of Apple iPhone
As you know, the Apple iPhone 6s inherent problem with spontaneous shutdown. The manufacturer acknowledged that the reason for this behavior are defective batteries, and run the program to replace them.
According to a source, the recent release of iOS 10.2 made the problem worse. Previously identified only in the iPhone 6s models a fault in the form of a turn off when a relatively high battery level (30% or even 50%) have now spread to other models.
An additional disadvantage is the fact that to cancel the upgrade and revert to a previous version of the OS impossible.