The battery percentage is shown beside the battery icon at the rightmost portion of the status bar at the top of an iOS device. Its off by default, but it can be enabled by going to Settings > Battery and turning on Battery Percentage.
The battery percentage indicates an estimate of the remaining battery charge on the device. But as has been noticed by some users of Apples latest smartphones, the iPhone 6s and the iPhone 6s Plus, it has been liable to get stuck at a certain percentage or not update with the correct indication even when the device is in heavy use.
Now, Apple has come out with an acknowledgment of the issue, suggesting that the problem has to do with the time settings on the affected devices. The company notes that the non-updating of the battery percentage is likely to occur if the time on iPhone 6s or iPhone 6s Plus is manually changed, or if time zones are changed when traveling.
Apple says that its looking into the cause of and a solution to the issue. But as a stopgap remedy, it recommends restarting the affected iPhone 6s or iPhone 6s Plus and then enabling the device date and time to be automatically set by going to Settings > General > Date & Time and turning on Set Automatically.
This temporary fix may not sit well, though, with users who are in the habit of manually changing the time settings on their iPhones. As noted by MacRumors from relevant threads in Apples support discussion forums, many of the users experiencing the issue are those who manually adjust their iPhones time settings in order to get around the timer-based barriers and eliminate waiting times in certain games.
While the issues relation to the time settings makes some sense, its curious that the issue apparently affects only the iPhone 6s and the iPhone 6s Plus.
In any case, a definitive solution to the problem is expected to be included by Apple in a upcoming software update, perhaps in the official release of iOS 9.3.