Battery Beeping

I've mentioned battery level testing before:

https://wb9kzy.blogspot.com/2026/05/low-power-battery-level-circuit.html

https://wb9kzy.blogspot.com/2025/01/good-old-sears.html

On a recent morning the smoke detector in the basement started beeping.  The Nimh battery was down below 7.5 volts - this corresponded to just entering the BAD region of the Sears VOM:

just a picture of the VOM, no test being done

So I think that's a good sign, two independent tests coming to the same conclusion, the battery is just going bad.  Although maybe it's just coincidence ?  The Craftsman 82411 VOM puts an 18 mA load on the 9V battery or about 500 ohms.  The voltage level at the top of the BAD range was measured at 6.75 volts so the droop down from 7.5 volts is from the load current across the internal resistance of the battery.

There is a W1FB article on a homebrew battery tester / VOM in the December 1992 issue of Monitoring Times:

for the 9V: 820 ohms versus 500 ohms (11 mA versus 18 mA) loads

source: https://www.worldradiohistory.com/Archive-Monitoring-TImes/1990s/Monitoring-Times-1992-12.pdf

W1FB has the load resistors selected but he doesn't comment about what the voltage ranges are for good and bad.  This looks like something I might try except maybe instead of the switches, have dedicated battery contacts for 9 volt and 1.5 volt AA ?  I'll think about it.

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