Change the auto-lock on iOS
One of the best ways to drain the battery on your smartphone is to leave the screen unlocked.
The more time your screen remains on, the more energy and battery power it’s using. If you never lock it, you’ll just be using up battery power that could be better spent on something else.
You need to change the auto-lock time to something like one or two minutes. To do so, head to the Settings app, and then choose “general”.
Down the screen, you should see the option to change auto-lock settings. In that page, change to whatever time you’d like – although either one or two minutes will be your best bet for saving power.