There is indeed an issue with all iOS 10 versions at this point still, and Apple customer care is finally beginning to admit this.They have admitted a coding error is being worked on and to watch for updates beyond 10.2.
I've done a good amount of research on LiPo batteries over the years (very similar to Lithium-Ion)
being an RC car racer among other hobbies. I believe what is happening is the OS is creating an extreme draw on the battery through some app corruption and those with marginal batteries hit a lower point of charge and the sudden voltage drop near the end takes the phone to shut off mode. My battery checks fine, and I never had the 30% shutdown, but I did have 10% per hour drain in standby mode while running nothing.
So, after people with marginally good batteries update, they kick in the high drain from corrupt iOS code and experience the shutdown, and those with decent batteries just notice a very short charge life and warm to hot phones. Now, that brings up an issue we all will have to watch for. Battery failure will now be more widespread since the #1 cause of battery failure is HEAT and rapid drain. My point is, keep an eye out for updates, and also watch for phone getting warm. Check Settings > Battery regularly and watch for offending apps causing high drain as the coding errors are still in our phones. I also recommend the free battery app called "Battery Life" (it is the green icon version as there are at least 2 with that name), and check your battery condition and temp on a regular basis to help reduce the chance of further failure.
Also keep in mind that the higher draining apps that you are running, then the worse the problems you will experience.
