One of the most useful tricks to save some battery on an iPhone is reducing the screen timeout, so the screen turns off quickly after iPhone being idle. To change screen timeout on iPhone 6 and other iPhones, do as follows:
1. Open the Settings.
2. Go to the General settings.
3. Scroll down to Auto-Lock option and tap on it
4. Now you should see some options to set as the screen timeout on iPhone 6.
5. Tap an option and you are all set
Tip: If you care about your battery life, it is recommended to set the screen timeout to 30 seconds or 1 minute.