Watch battery sudden death underground due to excess cell power draw?

I have a series 4 watch with 85% battery health. I recently activated cellular service and now have had several crashes after a subway commute to my athletic center pool (which is 2 stories underground).

The problem is identical to what's described here — after a bit of time in a low cell service area (in that question it was rural, in mine it is underground in NYC) — the battery suddenly screams about low power, indicated less than 10 percent charge, and crashes. At least once when this happened, the watch later corrected the battery reading to about 65 percent upon returning to the surface.

My only guess is that there is some bad code here that is turning up the power on the cellular radio in a desperate attempt to reconnect, and that power draw spike is throwing the battery capacity calculation off causing everything to go haywire.

I will try the Airplane mode fix, but this is clearly a software issue that can and should be fixed.

update: This issue also seems to in play, the watch turning to its own cellular after the phone is left behind. The problem almost always happens right after I leave my phone behind in the locker room.