If your iPhone is frozen and can't be restarted in the normal way press and hold hold down the home button and power buttons for up to 15 seconds. If nothing happens, ensure it is plugged in to a power source. If the red slider appears or the screen dims, keep pressing the two buttons until the Apple logo appears.
Another issue might be a recurring logo on start up. See the article below to remedy this.
Device not charging?
Check the lead and plug charge a different phone.
Check the charger port for any obstructions such as debris or fluff.
Remove any debris with a needle or SIM pin and then try using the cable again.
Some devices need at least 5 minutes on charge before the screen shows signs that the device is charging.
Battery & Performance
New iOS updates can throw the iPhone or iPad's battery calibration settings off, and it can take a few charge/recharge cycles to fix this.
For example if your iPhone battery is going from 17% to 3% percent in a matter of minutes - your iPhone or iPad might need a battery calibration.
Apple recommends that each month, you should drain your iPhone or iPad's battery completely and then charge it up until it's full. This process, called calibration, helps your device to estimate the battery life more accurately. Calibrating your battery will also help you know when you need to charge the battery.
We use diagnostic software to check the battery of every device to ensure it is operating in the optimal capacity range.
80% - 100% is the optimal capacity range.
Maximising Battery Life.
Recent updates to the iOS has caused significant battery drain on some devices.
Tips to maximise battery life:
1. Choose which apps you want to refresh in the background:
Go to Settings > General > Background App Refresh.
2. Enable low power mode
3. Update to the latest operating system
4. Charge without a case - especially if you notice your device is hot
5. Look in your Battery Usage log (Settings > Battery) to see how much battery life your apps are using
6. Turn down screen brightness on your phone
7. Set your device to sleep after 30 seconds of inactivity.
Settings > Display & Brightness > Auto-Lock (if you've got an old version of iOS, you may see Settings > General > Auto-Lock instead)
8. Turn off Bluetooth when not needed.
9. Turn off Wifi. This will stop your phone from looking for Wi-Fi networks to join when not required.
10. Turn off vibrating: Settings > Sounds & Haptics and turn off both of the vibrate options
11. Turn down the volume on your phone
Maximising Battery Life & Lifespan:
Understanding iPhone performance & its relation to your battery: