Today, Apple released iOS 9.2.1 update, contains the security improvement and bug fixes. iOS 9.2.1 is available for iPhone, iPad, and iPod Touch brings a fix for an issue that could prevent the completion of app installation when using an MDM server.
MDM (Mobile Device Management) server is used by the enterprise to manage and install apps remotely on the iPhone or iPad. This is an issue that appeared on iOS 9.2, where Apple also posted an article about it with the title “If apps don‘t finish installing with Mobile Device Management (MDM) and iOS 9.2”. In that article (which has been updated, today), Apple suggests updating the device to iOS 9.2.1 as the solution and a fix suggestion if there are some commands remain in the MDM server queue.
In iOS 9.2.1 update, it doesn’t mention a bug fix for ‘Battery Percentage Not Updating Issue on the iPhone 6s and 6s plus‘. It seems Apple will solve it on the next iOS update.
You can update to iOS 9.2.1 directly through your iOS device with the update size of around 40MB, depends on your device. You can read about the security content on iOS device with more details, here. If you have an iPhone 4s or later, iPod Touch 5th generation or later, iPad 2 or later, you are advised to update your device to this version.