Why is my iPhone 16 Pro Max randomly shutting down?

What was the battery state of charge? If it was below 20% that can be a possible cause. If that isn’t the case contact Apple Support to have your phone tested (they can do it remotely).

Best way: 

• Install the Apple Support app on your iPhone or iPad - you can contact support directly from the app, and the tech will have (with your permission) access to diagnostic data on your device

Other options:

• • Click on “Support” at the top or bottom of this page
  • Go to Contact Official Apple Support

(Note that both of the above have options to receive a callback or chat)

• • Call Apple Support; the phone numbers are in this link→Contact Apple for support and service - Apple Support
  • Make a Genius Bar appointment at an Apple Store→Genius Bar Reservation and Apple Support Options - Apple
  • Find an Apple store or Apple partner service provider→Find Locations

I’ve also had this issue. I barely purchased this iPhone 16 pro Max and have been having issues with it shutting down suddenly. When I turn it on, it’s at 100% battery and it shouldn’t be 100%. In fact it should be at 70 or even 60%. I also have a defibrillator implant. Anyway, I’m wondering why this is happening and why it is all of a sudden at 100% when I turn it back on.