Apple users have reported issues with the iPhone 6S battery percentage indicator, which appears to be stuck and not updating correctly. This problem seems to occur when the iPhone is switched to manual time and the time zone is changed. The issue persists even after rebooting the device and resetting all settings. Apple has acknowledged the problem and is investigating the cause. In the meantime, they have suggested a temporary fix. Users should restart their iPhone, then go to Settings > General > Date & Time and ensure that ‘Set Automatically’ is turned on. If the issue continues, users are advised to contact Apple Support. The problem does not seem to affect the phone’s performance or battery life, only the display of the battery percentage.
Go to source article: https://discussions.apple.com/thread/7297543?tstart=0