Low Battery Alarm when disarmed

Ran into an issue that we have not seen before.
We had an aircraft running on battery power doing some extended ground testing of other functions and the battery ran flat with no battery alarm going off. To be clear the AC was disarmed the whole time and hot not been armed at any point.
All battery alarm settings are configured correctly and the buzzer functions.
Reading the documentation the FC should always activate the low battery alarm no matter the state of the aircraft.

Was the FC connected by USB? When the USB is connected, Ardupilot assumes you’re doing bench testing, so it does some things like disable the battery alarm and dim the LEDs.

Oh never knew that was a feature. But no, USB was not connected.
As a test i powered everything up and then just wound the bench top power supply well past low and crit voltage levels and can reproduce the no buzzer scenario at will.

Huh. To diagnose, it would be easiest to give us a log. Try this:

  1. Turn on disarmed logging with LOG_DISARMED = 1
  2. Boot the drone up with your power supply at normal battery voltage
  3. Lower the supply voltage below your configured thresholds
  4. Turn off disarmed logging and download the log

This will make it easy to see if your failsafes are correctly being triggered and your sensor values are normal.

On it!
Same results, no low battery alarm. I did recognize the low voltage pre-arm warning, we haven’t run into that warning in normal operation before. I did attempt to arm the AC after I it was below the pre-arm voltage threshold and it would reject the arming command so that works.
Log is at the end of the follow Onedrive link

Well, the few hypotheses I had didn’t bear out. Not sure why your alarm isn’t going off. I did find it interesting that there are low voltage messages being recorded in the log, but they only start once the voltage goes under 35V, which is not your configured values of 36V or 38V, so I don’t even know where those are coming from.

In my experience, it does sound the alarm even if the drone is disarmed, although I have never used multiple battery monitors.

Interesting observations. On previous firmware versions it has alarmed when either battery monitor has gone below the low battery threshold.
We do not have a here GPS on these AC so I should plug one in to check if the status LED’s change as well. That would help narrow down the problem to just the buzzer output or the alarm state in general.
I should also do the same tests but with the AC armed and the motors spinning to see if there is any difference.

Thank you for your help as well