If you do not know on your iPhone 6S with iOS how to activate the energy saving mode, then this article should help you. Because the power-saving mode allows you to optimize the battery consumption of the smart phones and leads to longer battery life.
To activate the power saving mode on the iPhone 6S, you need to navigate into the following submenu of iOS 9.
1. Open the menu and then the Settings
2. Navigate to: battery
3. Enable now by using the slider the saving of battery power.
You have now successfully activated the energy saving mode of your iPhone 6S. You recognize this by the fact that the battery indicator is now yellow.