Here is how you can fix iPhone 6/6S Plus bug of not showing correct battery percentage level
If you have purchased Apple’s iPhone 6 or iPhone 6S Plus, you would have noticed something amiss with your battery percentage levels. In both the smartphones from Apple, the battery level does not update when charging or during normal use. This was pointed out to Apple which has stated that this is a known bug and they are working on a fix.
According to an advisory released recently, Apple says that it’s just a time zone bug and states that a patch is on its way. According to Apple, the problem occurs when you set the time zone manually or you change zones when travelling from one location to another.
iPhone 6 and 6S Plus users have reported that the battery percentage remains unchanged if you use the device for a longer period of time or when charging. In most cases it takes a few minutes to refresh and show the correct charge level.
How to fix it
Go over to Settings > General > Date & Time and enable the option that reads “Set Automatically.”
The problem with the battery level in iPhone 6 and 6S Plus was first reported back in September when the first buyers received their new S models.
At that time taking the iPhone to the Apple store was the only solution however with the above workaround you can fix the bug till the time Apple issues a patch.