Users on an Apple forum report that the battery indicator jumps from 30% to 1% (dubbed the 30% bug) and a reboot is required. The phone then runs for a few more hours. Some have taken the iPhone back to receive a replacement only to find that the same thing happens.
Apple has not responded to the 11 pages of forum complaints but apparently, Genius Bar staff have identified unusual discharging of the battery – which does not make sense if a reboot temporarily fixes the issue and returns the battery indicator to 30%. It also appears to affect all versions of iPhone that support iOS 10.x.
Users have tried downgrading to 10.1 and upgrading to the 10.2 beta, but the problem remains.
In a related issue the Daily Mail Australia states:
“Apple vowed to fix a technical issue that has seen some iPhone 6s handsets shutting down unexpectedly. The Cupertino-based technology firm will replace batteries on affected devices, it said. The issue only affects a 'relatively small batch' of the devices manufactured last year, says Apple, but the company would not disclose the exact numbers. This is Apple's second iPhone repair program in less than a week after it announced that it would fix the 'touch disease' issue, albeit at a charge, blighting many users' iPhone 6 Plus handsets.”