Same problem but here's the answer. I wanted more detailed maps so I downloaded a map from http://garmin.openstreetmap.nl/. Then I opened up the back of the Nav 5 and removed the memory card. I dropped the the .img file from http://garmin.openstreetmap.nl/ on the memory card masking making sure the file name doesn't clash with the original maps. When you fire up the Nav 5 again it scans the memory card and loads all the maps, same thing in Basecamp. I'm used to doing this with my Garmin cycle computer, works a treat and saves a fortune. Enjoy

Same problem but here's the answer. I wanted more detailed maps so I downloaded a map from http://garmin.openstreetmap.nl/. Then I opened up the back of the Nav 5 and removed the memory card. I dropped the the .img file from http://garmin.openstreetmap.nl/ on the memory card masking sure the file name doesn't clash with the original maps. When you fire up the Nav 5 again it scans the memory card and loads all the maps, same thing in Basecamp. I'm used to doing this with my Garmin cycle computer, works a treat and saves a fortune. Enjoy