Use Low Power Mode to save your iPhone’s battery life
Low Power Mode reduces the amount of power that your iPhone uses when it’s on low battery.
To turn Low Power Mode on or off; Go to Settings > Battery, and toggle Low Power Mode On or Off.
You can also turn Low Power Mode on and off from Control Center. Go to Settings > Control Center > Customize Controls, then select Low Power Mode to add it to Control Center.
When Low Power Mode is on, your iPhone’s battery lasts longer before you need to charge it, but some features might take longer to update or complete. Also, some tasks might not work until you turn off Low Power Mode, or until you charge your iPhone to 80% or higher.
These features are affected by Low Power Mode:
- Email fetch
- “Hey Siri”
- Background App refresh
- Automatic downloads
- Some visual effects
- Auto-Lock (defaults to 30 seconds)
- iCloud Photo Library (temporarily paused)
When Low Power Mode is on, the battery in the status bar will be yellow. You’ll see 
and the battery percentage. After you charge your iPhone to 80% or higher, Low Power Mode is turned off automatically.