Turn on battery saving mode in iOS 9
To activate the mode you should go to the new section of Battery Settings menu in beta or final iOS 9. You'll find different options regarding battery and one of the toggles allow you to enable or disable saving mode battery. When you activate this mode, the battery icon changes from green to yellow. You will notice that the iPhone screen becomes darker and turn off certain functions or operate with a lower refresh rate. Among them, the apps in the background, automatic downloads and visual animations.
When the mode battery saver is activated we are also forced to see the battery level in yellow, a way of warning not to forget that we are squeezing the most of the iPhone battery and thus reduce the level of demand of processing mobile.
Normally this type of savings will allow us to continue using the device but with reduced connectivity to mobile data networks. We can always make calls and send text messages, but the performance of the device will not be the same as when the device is charged at 100%.
The power saving mode in iOS 9 is a very important function in mind those who use the iPhone all day, because there are always times when we ran out of an area where connecting the charger. Now we can use a few extra hours of battery life, but we will notice a significant reduction in device performance.
In early versions betas battery saving mode dramatic improvements in runtime are not managed, but Apple guarantees that with the official arrival of iOS 9 can get between 1 and 3 hours of extra battery.