Are you an iPhone 6s, 6 Plus, or 6s user and has your battery been randomly shutting down? If so, this is pretty common because there have been widespread reports of this problem. Apple has launched an iPhone 6 Battery Replacement Program but not all iPhones are eligible for this program. The random shutdowns have been known to be caused by a software bug which can be simply fixed by upgrading to iOS 10.2.1.
If you are facing this problem, don’t waste your time going to the Apple store and simply just upgrade your phone.