I didn't see your original post. I don't think there's any way to turn off the maps, so something isn't working correctly. I replaced my 705 battery, and that didn't cause any problems for me.

Plug it in with the USB cable. On Windows, my 705 shows as Garmin (E : ) and Garmin4GB (F : ). I think I renamed the 4GB card to make it easier to see which drive is the 705, and which is the card.

The map file
On the card, you need a file named
gmapsupp.img
in the folder named GARMIN

need a new file? garmin.openstreetmap.nl/

Years ago, I downloaded the eastern US file (2GB in size) and renamed it to gmapsupp.img, and copied it to the 4GB card.

Try scan and repair
Right click the drive letter, select Properties-->Tools. Click Error Checking. It may say "you don't need to scan this drive, we haven't found errors" but click Scan and Repair. It'll take a minute to finish. It'll either say it's okay, or list the sectors it repaired.

I used to have to do this regularly on the base 705 drive, or I'd get occasional mangled ride recordings. It seems to be better now (maybe with the new battery?) I've never needed to scan the 4gb card, since it only holds the map file.