Make sure that your iPhone’s data and Wi-Fi are on and connected
Open Settings -> General -> Date & Time
Toggle the switch for Set Automatically Off and On again. The switch will turn gray, then green.
Date & Time - iOS
Restart the iPhone by holding down the Sleep/Wake and Home button until you see the Apple logo
Once your device has restarted you should see the battery icon back to normal. Some users have also said that simply messing around with the date and time can also temporarily fix the error. Simply, toggle Set Automatically ON/OFF multiple times, or switch time zones as well.