IPhone restart itself randomly

The wrong battery was installed in the phone.

Take the phone to an Apple Store or authorized Apple Service shop to see if they can help. Please understand that they may refuse to work on the phone because an unauthorized person....you....tampered with the phone.

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If you replaced the battery yourself you may have installed a poor quality after-market battery. Using the phone on a cellular network puts a larger strain on the battery than just using Wi-Fi, so it is likely that the battery was not of good quality.

You don't have to go to an Apple Store. Check the link that I provided to find an authorized Apple Service shop.

You won't be able to install the Apple battery yourself, you have to have it installed.

No one other than an Apple engineer can interpret diagnostic logs, and even they don’t read them directly. They process them with an AI app that interprets the meaning of the log contents. In general a “panic” in Unix (and iOS is a Unix derivative) is an unexpected error that could not be recovered from except by restarting the app that caused it or operating system.

I can’t tell you how to choose a good quality battery in your location. The best choice it to have Apple replace the battery, or an Apple Authorized Service Provider if Apple doesn’t have a presence near you. If the aftermarket battery costs significantly less than USD 40 (in local currency) it is almost certainly low quality. If there are no Apple or authorized repairers in your location you will have to take your chances.

Go to Settings/Battery/Battery health and review what it says, as well as the maximum capacity. That symptom usually indicates a weak battery.

If you changed the battery yourself, you probably put in a poor quality battery.

Task 0 in Unix is the operating system itself; that is, iOS.

It doesn’t matter who replaced it, they replaced it with a defective battery. Take if back to whoever replaced it and tell them that.