It's always a question mark ('?') on my 520 when I add the battery field. Is that not the battery status of the Varia?
If it's something else (headlight?), is there a way to get the Varia taillight battery status on the 520?
Is the Varia (RTL) configured as part of a light network as well as being added as a radar unit?
The light battery status is the status of the battery with the lowest value that is part of the light network.