Apple has confirmed a bug that iPhone 6s and 6s Plus users have been reporting for months: In certain cases, the battery indicator on the phones isn't accurate.
Users on Apple's community support forums have been reporting that their battery indicators haven't been updating properly, occasionally leading them to run out of juice when they've incorrectly thought they had enough charge.
According to a page on Apple's website, the problem seems to affect users who travel between time zones. For whatever reason, when the time zone switches it prevents the battery indicator from updating properly. The company said that it's working on a fix but didn't specify when users can expect the problem to stop.
If you're having trouble, Apple recommends the following steps:
Restart your iPhone. Go to Settings > General > Date & Time and make sure that Set Automatically is turned on. Learn more about the date and time on your device.