Why does my iPhone shut down at 50% battery?

Well your battery continues to die until it reaches 0%, then when you charge it goes back up to 100%, that is how a battery works. If you mean your iPhone is shutting down when your battery reaches 50%, that is the symptom of a battery issue, usually because it's significantly degraded. In that case, you should visit your nearest Apple Store's Genius Bar or an Apple Authorized Service Provider for diagnostics and your service options.

Apple Store Genius Bar: Genius Bar Reservation and Apple Support Options - Apple

Apple Authorized Service Providers: Find Locations - Apple

"Why does my iPhone shut down at 50% battery?: Why my battery is dying at 50"

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iPhone Shutting Down t 50% Battery:

View the Battery Health:

Apple recommends you get a new battery, once the Battery Health below 80%. So, see if it is time for a new battery

1. Go To: Settings
2. Tap: Battery
3. Tap: Battery Health
4. View: [the percentage]
5. Is it Below 80%?  If so, it is time for a new battery