The sound of Feet of Clay in the middle of the night ?

Tenergy 9V batteries have been mentioned before:

https://wb9kzy.blogspot.com/2022/01/our-friend-9-volt-battery.html

Yesterday I decided to change the Tenergy 9V in the downstairs smoke alarm with a freshly charged one.  However in the middle of the night I started hearing the alarm do the battery low beep about every 40 seconds.  

I don't know if it's the new battery or the charger or both.  I hate it when good stuff stops working - especially when I was trying to be proactive !

I've got a different charger, no smarts, doesn't try to sense delta V or any of that, it just puts out a constant 16 mA, maybe that'll work better.  So I recharged the removed battery for a couple of hours.  Terminal voltage is well over 9V.  One good thing about the other charger: no RFI, the Tenergy is terribly noisy.

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm