My Nokia Lumia 820 keeps shutting off?

My Nokia Lumia 820 phone was updating and all of a sudden it shut off and when I restart it it goes to the update screen for a few seconds and then shuts off again. I am almost certain it cannot be my battery as I placed it on the charged for an hour and it keeps coming on and shutting off every minute or two. I don't know what to do. Can I get some advice please?
Added (1). My Nokia Lumia 820 phone was updating and all of a sudden it shut off and when I restart it it goes to the update screen for a few seconds and then shuts off again. I am almost certain it cannot be my battery as I placed it on the charger for an hour and it keeps coming on and shutting off every minute or two. I don't know what to do. Can I get some advice please?

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