iPhone XR Dead, but Boot Loops on Charger? Dies when unplugged.

@oldturkey03 is right about a new battery. In situations like this we completely rule out a parts issue, to do this we would install the logic board into a known good housing with known good screen and battery.

If you haven’t got another housing you will need to disconnect all the flexes except battery, screen and charge port, check results and go from there. If your phone is paired to your PC or Mac you can also disconnect the screen so as only the battery and charge port are connected and see if it is recognised.

If you removed the logic board while replacing the glass it will most likely be a parts problem.

I have run into this issue with a lot of iPhone's e.g. 7+, 8+, X, Xr, etc. I read somewhere this is the bootloader failing a 'self-test' so it just loops. This always works for me ****beware this will completely wipe any data***** Anyways if you put your phone in DFU mode [plug phone into mac or pc(any computer with iTunes) press/release volume up, then press/release volume down, then press/hold power, keep holding power through the apple logo, once the 'connect to iTunes' screen appears then you can release the power button]. The iTunes program will alert you that a phone needs to upgraded or restored. Select restore and follow the onscreen instructions.

the best thing to do in this situation would be to erase the phone. if you have an iCloud backup you can redownload your data after. and then follow the instructions on the apple website for resetting your phone.

if It is an issue with the battery, buy the iFixit replacement kit and replace it. this might solve the problem.

I hope this helps.