The update didn't completely exterminate the bugs, but Apple claims that with the release it has seen a decline in the number of iPhone 6s shutdowns by 80%. The update has lowered the number of shutdowns on iPhone 6 models by 70%. These sizeable reductions have taken place after iOS 10.2.1 has been installed on over 50% of the units that received the update.
Besides including a power management patch, iOS 10.2.1 also includes a new feature that allows those whose iPhone shutdowns suddenly due to an older battery, to instantly reboot by simply pressing the power button. Previously, an affected phone would have to be connected to a power adapter in order to reboot. This issue apparently has nothing to do with the battery problem found on some other Apple iPhone 6s units. Apple is replacing the battery on these specific units for free since they have a habit of shutting down even with 30% of life remaining on them. When these batteries were manufactured, they were exposed to too much ambient air which is believed to be the cause of the problem.
We also added the ability for the phone to restart without needing to connect to power, if a user still encounters an unexpected shutdown. It is important to note that these unexpected shutdowns are not a safety issue, but we understand it can be an inconvenience and wanted to fix the issue as quickly as possible. If a customer has any issues with their device they can contact AppleCare."-Apple