Phone stuck in bootloop after battery died… coincidence or not?

The phone likely died while Android was writing system/cache files and it corrupted the OS, so now it can’t finish booting and just loops.

Try charging it a good while first, then go to recovery and do a factory reset. If it still bootloops, you’ll need to re-flash the stock firmware (Odin/Fastboot depending on the phone).

Happens a lot when phones shut off at 1–2% battery.

Low battery shutdowns can corrupt stuff, especially if it died while writing data. Happens more than people think.