iphone keeps restarting
why does my iPhone keeps restarting itself and after restarting the battery remains 1% and then automatically changed to its battery level .
1) At first the iPhone restarts automatically
2) after restarting the battery shows 1%
3) after few moments 1% increases to its battery level
4) battery keeps fluctuating up and down
iphone 6 plus
64GB
ios 12.4.7
iPhone 6 Plus, iOS 12