What are some reasons an iPhone might turn off?

 some reasons an iPhone might turn off:

• Faulty apps, water damage, or (typically) battery difficulties can all cause an iPhone to continually turning off. An iPhone that keeps turning off or power cycling on its own can sometimes be fixed with a hard reset. If all else fails, contact Apple Support for a battery change to prevent the problem from repeating.
• If your iPhone shuts down at 30% battery, there are two ways to know for sure if the battery is the issue: the Battery Health feature built into iOS, and a tool offered by Apple.

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