There are multiple versions of this device so does yours take (2) AAA or (1) CR123A?
The device requires close to 3V to run properly so the manufacturer doesn’t recommend using rechargeable batteries.
Does the device show that there are pending changes?
Every time I’ve had a device join like this, removing it and bouncing the hub solved the problem.
Users on a different platform were having similar inclusion issues with this device and after watching the inclusion process with a z-wave sniffer I discovered that the device sometimes sends a wake up notification which causes the handler to put the device to sleep before inclusion finishes.
I wasn’t aware users were having the same problem with my ST handler, but now that I know I’ll make some changes to the handler tonight.
All that being said, that shouldn’t have anything to do with the battery draining. If you’re not using rechargeable batteries then you should be getting at least a couple of months out of the AAA or even longer with the CR123A and the 17.9 firmware.
If you’re only seeing this with one sensor you might want to contact The Smartest House’s support.