DC voltage not displaying

Hi--
We have a Garmin GPSMap 942sx running off a 24V battery but connected to various antennae and other devices by a backbone powered by 12V. We are troubleshooting issues on the 12V battery. When the battery powering the backbone gets low, the Garmin GPS shows a low voltage warning with a number (e.g., 9.7v). I can look at the warnings log and see times of errors. However, I wanted to add the DC power voltage to one of the corner squares. When I do so, the voltage is dashed out. There is a box for the data but instead of numbers, there are dashes. It seems as though, since an warning of low voltage with the actual voltage being sensed is displaying, we should be able to display on the overlay. Thoughts? Thanks in advance

 

Hi--I got my answer from Garmin chat. You can display the system voltage, which in our case is 24V (need to click on system before entering DC voltage to get the right display) on the menu that puts data in the corner squares. There is no way to get the voltage of the backbone (even though the Garmin will display an error with the voltage reading of the backbone).