Same question here. I have to assume this would either work by the device sending out a last gasp "I'm about to die" GPS location call home (for finding it when it's far away), or else there's a mostly passive RFID-like thing in the phone that makes it findable by nearby devices (for finding it when it's somewhere in the house/car/office with you).
I read that they use bluetooth beaconing for this. A simple bluetooth beacon like a tile can run for months with minimal power. The phone isn't actually 'dead dead' it's still powering the bluetooth beacon.
If it is using a similar technology to AirTags, then it could broadcast signal for a long time on remaining battery. Even Bluetooth can do months on coin cell battery.
Moto g30 without cell modem but with enabled WiFi easily gets two weeks of the runtime without much of display time.
My RAZR MAXX could sit for months on the one charge (with already busted battery) without any cell activity.
So if you don't need the display and a hungry wireless tech to keep on constantly you can have enough juice for days, even when the phone is no longer in the power profile to have a full run.
