After a plethora of complaints, Apple this week has posted a new support document acknowledging an issue with the iPhone 6s and iPhone 6s Plus that causes the battery percentage indicator in the status bar not to update as the battery itself drains. This means that the battery percentage icon could display that you have much more battery life left than you actually do.
In the support document, Apple addresses the issue and assures iPhone 6s and iPhone 6s Plus users that it is working on a fix. Weirdly, the company says the issue is caused by time zone changes, whether done manually or automatically while traveling
If you change the time on your iPhone 6s or iPhone 6s Plus manually or change time zones when traveling, you might notice that the battery percentage doesn’t update. Learn what to do.
As far as fixes go, Apple says that restarting your device should temporarily cure the problem, as should going into Settings > General > Date & Time and ensuring that “Set Automatically” is enabled. Obviously, the issue here is that you may not realize the battery percentage number hasn’t changed for awhile, so it would be hard to know that you need to reboot or check your Date & Time settings.
Nevertheless, Apple says it is aware of the issue and is investigating the cause and a solution.