I had gotten into the habit of charging it on Tuesdays, charged it on August 8, tried to charge it on August 15, and it wouldn't acknowlege the charging cable. Since the device needs to be on the cable to reset, there was nothing for it except to let the battery discharge. Tonight, at 8:10 PM, it synced for the last time, and went dark. I have it sitting in a bottle full of desicators, and I will try to charge it again next Tuesday, but I am not hopeful.
It makes me a bit sad; for three and a half years, that thing was with more more than ANYTHING. And now it's gone, probably. Fitbit has given me a courtest 25% discount on a new device, and it is on order. Life goes on.