If You Really Want to Save Battery, Use Airplane Mode

Airplane mode is a feature that will shut down all forms of connection from your iPhone. Sure, it might seem excessive, but using this will ensure that your battery lasts as long as possible. 

To use Airplane mode, all you need to do is open your Control Center and toggle Airplane mode on. This will get rid of any connection you didn’t even think about, like using your iPhone as a Hotspot.