I just happened to catch this in my live logging today. Never would have know this was the case if I didn’t.
It seems the Sensor sends one notification that your battery is low and never sends another.
When I saw this I remembered that about two weeks ago I had an alert notification in my Android Smart Things app about this sensor having a low battery. I had cleared it thinking I would deal with it the next time it occurred. Then I forgot and now I see another alert will never be sent.
It seems to me the low battery level alert should repeat. Perhaps once a day ?