3-minute boot loop, with a black Apple logo. Help?

After battery and screen replacement on my daughter’s 5S (my first time with IFIXIT), the phone just keeps rebooting (boot looping) at about 3 minute intervals. Black apple on white screen, but nothing else, which is evidently rare. Virtually all the boot looping cases I’ve found in forums involve other recurring problems, like blue or red screens or bars, and often the answer is based on the color or bar issues.

The new IFIXIT battery was charging slowly and discharging fast, and its displayed charge level was erratic, but that problem cleared up when I put the old/original battery back in.

I’ve followed all the advice that seemed to apply, but nothing gives me more than 3 minutes of phone use at a time.

I have until tomorrow to get this thing working or get a new phone, which feels like accepting defeat after so many hours of repairing and troubleshooting.