thanks @Chelsea_Ring for the suggestion. Ok so I found another battery to try with this sensor. I did a factory reset of the sensor, then reinstalled the sensor to my system and with the other battery in it seems to be working now, after a couple days the battery icon in the app is still full green. I will see how it goes, checking the battery status over the next while.
however one strange thing I just noticed this evening. While sitting here at my desktop computer, I can see the contact sensor which had the battery problem. The door on which it is mounted is fully closed, and the app reports the door is closed.
But just now I saw the blue LED on the contact sensor flash quickly a number of times (maybe around 6-10 times in rapid succession). I thought that strange, as the door is still closed solidly shut. Then a few minutes later, it happened again - the blue LED flashed rapidly a number of times then stopped. No door chime, no change in status in the app - nothing to indicate the door was opened or sensor status changed. I’ve not noticed this blinking before (maybe just obvious now since it’s night time and I happen to be sitting near the sensor). I wonder if the contact sensor is acting up and causing unexpected drain on the battery?
is there some normal reason to see the blue LED on a contact sensor blink rapidly when the sensor is closed and not moving?? What does that blinking mean?
As I mentioned, the door is solidly closed and app doesn’t report the contact has ever opened since I re-installed it (and yes, I tested that it works correctly when I re-installed it, and the magnet is mounted well within the specified mounting distance).