Why does my phone keep restarting and then dying?

My phone (I have an Iphone 5s) suddenly died and then restarted. It died before it could restart and then started to restart again. The cycle keeps going on and on. I don't have an old battery and worked perfectly until now out of the blue.

That it back to your phone carrier & ask them. Sounds fatal…

What percentage does it show? Try take it to an apple store to replace the battery as they degrade over time and lose their ability to hold power for long.

It must be updating

I would recommend backing up and restoring. However given the age of the phone I suspect the battery needs to be replaced.

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