Apple is investigating a bug that makes the iPhone misreport how much battery it has
The misreporting occurs when a user changes time zones automatically or changes the time on the device. This can be a problem when travelling abroad as the iPhone will report an exaggerated amount of charge.
Apple suggests that customers who are affected restart the iPhone and check the time is being set automatically, rather than manually. A user can do this by going to Settings > General > Date & Time.
Apple doesn't give a time frame for the fix, but a new version of iOS - 9.2.1 - could be coming soon, and the company recently released details of iOS 9.3, the next major update to the operating system. The bug fix could be contained in either two of these updates.