According to the notification,
This iPhone has experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power. Performance management has been applied to help prevent this from happening again.
Your battery is failed and your phone is going to run slower now so the phone doesn’t power itself off.
TechFreeze t1_j1drgq4 wrote
Reply to What caused this? by TrashAtEverything_
According to the notification, This iPhone has experienced an unexpected shutdown because the battery was unable to deliver the necessary peak power. Performance management has been applied to help prevent this from happening again.
Your battery is failed and your phone is going to run slower now so the phone doesn’t power itself off.