Kinda surprised non of the 4DTV 'guys' have jumped in here yet. I'm not a 4DTV guy myself, but from what I've garnered from the threads, I'd say don't unplug your unit unless the battery has already been replaced. Check the numbers on screen and on the label on the back do match. Think details can be found with a site search(I don't remember the 'details' of the procedure to get the onscreen numbers) If they match, replace the battery without unplugging the unit to retain the numbers. (guess you'd have to do that to be able to ship it to someone)
If they don't match, it can be used as a dish mover and get some ITC 4DTV with the new maps, but subscribing is impossible..
Being I'm not anywhere an authority, subject to correction, except pretty dang sure don't unplug the unit until the battery is replaced especially if intending to subscribe.
The last place suggested to send a receiver, unfortunately, has ended service
http://www.satelliteguys.us/threads/316581-ATS-Electronics-going-out-of-business
After that don't know if one of the 4DTV 'guys' could do it (I read the shipping of those is $$) but most likely could 'talk you thru the procedure. I'd suggest reading the stickies pertaining to it in this C band section of the forum