my iPhonekeeps shutting down whenever i open an app. I need to plug it in to reboot.

You may have a poor battery condition which cannot provide sufficient power for peak performance. What is the Battery Health of your iPhone? Open Settings ➔ Battery ➔ Battery Health and let us know which percentage you see for Maximum Capacity. Also note what is written under Peak Performance. If your battery's Maximum Capacity shows a value of 80% or less, then it has gone through its lifecycle and therefore should be replaced, according to Apple.

Axel F.