I decided to manually track each time I had to replace the batteries for a few of my devices to see if I could see any interesting pattern(s).
Master Bedroom Window: 12/10/2023, 01/01/2024, 01/26/2024, 02/17/2024.
Kids Bedroom Window: 12/28/2023, 01/21/2024, 02/17/2024.
Guestroom Right Window: 12/29/2023, 01/25/2024, 02/17/2024.
Dining Left Window: 12/30/2023, 01/26/2024, 02/20/2024.
Dining Right Window: 01/03/2023, 01/25/2024, 02/20/2024.
Basement Living Room Window: 01/03/2023, 01/21/2024, 02/20/2024.
Basement Kitchen Sink: 12/15/2023, 01/06/2024.
Basement Kitchen Window: 01/06/2024, 02/05/2024.
Office Window: 12/17/2023, 01/08/2024.
Garage Freezer: 01/10/2024, 02/20/2024.
Guestroom Left Window: 01/13/2024, 02/05/2024.
Kitchen Left Window: 01/15/2024, 02/16/2024.
Basement Bedroom Window: 01/16/2024, 02/16/2024.
Kids Bathroom Window: 01/18/2024, 02/17/2024.
Kitchen Middle Window: 01/19/2024, 02/16/2024.
Master Bathroom Window: 01/19/2024, 02/17/2024.
Large Garage: 12/25/2023, 01/24/2024.
Basement Toilet: 12/29/2023, 01/25/2024.
The only interesting pattern I see here is that this proves me wrong when I previously said I was getting 10 to 15 days out of the batteries… as you can see, it is more like 20 to 30 days. 
It is also worth noting that the batteries in many of the furthest devices away from my hub seem to last much longer (all the same battery type/brand)… seems like it would be the opposite:
Mailbox: 05/15/2023 (Approx.), 02/16/2024.
Shed Door: 07/15/2023 (Approx.), currently reporting 44% as of 02/21/2024.
South Gate: 07/15/2023 (Approx.), currently reporting 33% as of 02/21/2024.
North Gate: 11/21/2023 (Approx.), currently reporting 100% as of 02/21/2024.
Almost all of the listed devices (all but 3) are using the driver from Mariano_Colmenarejo. The generic SmartThings driver performance was much worse.
Recently, I had to leave unexpectedly for 4 days to go to a funeral, and by the time I made it back home, more than 50% of all off my battery powered devices were offline with dead batteries (not all are listed above). As was previously said, the batteries used to last more than 1.5 years.
I can’t imagine trying to monitor a vacation rental property or family cabin with SmartThings anymore, at least not with any battery powered devices. As I recall, I think that was how SmartThings was born… so maybe it’s time they get back to their roots! Is there any hope for the future of SmartThings as a viable home automation system? (rhetorical question)
Yikes, this does not instill confidence that they even know what the issue is, let alone that they may actually be able to get it fixed soon. 
