Apple posted a support page about this battery-update issue for the iPhone 6S and 6S Plus on January 13. “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,” it begins. “Learn what to do.”
The suggested steps are to restart your phone, then go to Settings > General > Date & Time and make sure that “Set Automatically” is toggled on (i.e., so that green is visible to the left of the on-screen slider button).
“If this happens again and you didn’t change the time or time zone on your device, contact Apple Support,” according to the support page. “Apple is aware of this issue and is investigating the cause and a solution.”
While Apple acknowledged the issue earlier this week, it appears that iPhone 6S and 6S owners have been reporting the issue since the devices’ were released last September.
“Many of the users experiencing the issue had been manually adjusting their phones’ clock settings in order to bypass timer-based barriers in certain games, and Apple’s suggestion about ensuring the time is being set automatically indicates the battery issue is indeed likely related to clock settings,” according to MacRumors.