New iOS 9 Feature - Low Power Mode
"Low Power Mode" has now been added to iOS 9. Low Power Mode, like "Power Reserve mode" on Apple Watch, turns some features off on your iPhone to conserve battery consumption. The feature would be useful in such situations the battery life is low but you cannot charge it because no charger is available while on the go.
※ Limited features in Low Power Mode
Low Power Mode disables Mail fetch, background app refresh and download, and some motion effects. It also reduces screen brightness, and Auto-Lock time to 30 seconds. Besides, allegedly, some tasks on the iPhone in Low Power Mode may throttle down its CPU performance by around 40%.
Open "Battery" in "Settings"
In the "Settings" App, tap the newly added "Battery" section.
Enable "Low Power Mode"
Toggle "Low Power Mode" to on, and tap "Continue"
Battery icon goes yellow
The familiar Battery icon turns yellow indicating that you are using Low Power Mode.
When you charge your iPhone in Low Power Mode, upon reaching 80% charge, the mode will be automatically turned off.
Apple says that iOS 9 is designed to save battery usage on the iPhone wherever possible. For example, when your iPhone is facedown on the table, with ambient light and proximity sensors, the device detects if it is facedown on a surface and stops the screen from turning on even when a notification comes in (iPhone 5s or later).
These detailed specifications of iOS 9 are to help extend your battery life by around one hour even in the normal power mode.