If you have an iPhone 6 or 6s, there’s a chance you’ve been plagued with random shutdowns. Apple has a replacement plan in place that gets you a new battery, but if you haven’t gotten around to that yet, you’ll be happy to hear that the newest version of iOS 10 seems to have fixed the problem.
Source: LifeHacker – iOS 10.2.1 Is Reducing Those Pesky Random Shutdowns for iPhone 6 and 6s Owners