This IS what has happened here - If you look at the Headquarters Menu (quick key H) you will see the unit AZ0 the battery command has a red R in the radio coloumn indicating it has a radio but is out of contact.
Play a couple of turns and it comes back "on line"
I have played I couple of turns, artillery radio "R" is not in red, and it is still unavailable in the artillery screen I attach another save file (turn 8)