Unable to Update Maps - Out of Memory

The critical files are the map files, your Etrex will work without problems when the card is removed.

I'd like to believe that you're correct, but when the official software states "if the card is removed, your device will not work" and I have two Topo Pro cards that cost over Euro 100 each, (which I use every time I hike) I can't take the risk.

Thanks for your suggestions though.

'Seems that by releasing a 7.67GB map update Garim have in effect rendered the eTrex obsolete.

Well your call, but it'll work if Express allows you to download the map to your PC, unfortunately that's not always the case but you could at least try.

As for a map update rendering your Etrex obsolete that is simply not the case, your issue is the fact you have sd cards preloaded with maps that you wish to use, which means that if possible you need to do what I'm suggesting above to install a portion of the specific map you want to install on your device.

Failing that you'll just have to keep swapping cards.

I copied the entire /Garmin folder from my eTrex to a microSD card plugged directly into my PC, which resulted in Garmin Express "seeing" the microSD card as an eTrex and allowed the update to go ahead.

After more than six hours of update, I have the following:

Prior to update:

gmapprom.img TopoActive Europe West v4 3.4GB

gmapprom1.img TopoActive Europe East v4 2.3GB

Post update:

D6185060B.img TopoActive Europe 2019.10 South West 2.9GB

gmapdem.img Garmin DEM Map EU 919MB

gmapprom1.img TopoActive Europe 2019.10 North East 3.3GB

..which makes me think I might be able to delete the old maps on the eTrex and copy the new ones over - would this work or would some kind of copy protection prevent it?

I don't have your map to check but it should do, a locked map would come with additional files ending in .unl or .gma so look for files named gmapprom1.gma, gmapprom1.unl, D6185060B.gma, D6185060B.unl

If those files exist copy them across too, and keep the original map files on your sd card just in case as a backup so you can copy those files back if necessary.

I copied TopoActive Europe 2019.10 South West and TopoActive Europe 2019.10 North East from the microSD card to the eTrex and I can see both maps in BaseCamp from the eTrex so things seem to have worked.

Garmin Express still believes that the maps have not been updated, but perhaps that is because there was no room to copy Garmin DEM Map EU to the eTrex.

I believe that the "t" in eTrex 35t stands for the TopoActive maps that came pre-installed, so it does not seem logical that they cannot be easily updated. The most recent equivalent looks to be the Oregon 750t, which, since it does not have more internal memory than the eTrex, is likely to have the same problem.

I think you said it was just the latest map that caused you issues, and that's really only because you have other maps on cards that you've bought. If you read what Garmin says about maps on cards, and also about future map updates, this should have been known to you. The main thing is you now know how to resolve it going forward. 

I' ve been unable to find what Garmin has to say about future map updates.

The eTrex was recommended by the local Garmin agent for hiking, but there is often not enough detail for hiking on the maps that come pre-installed. This being the case, I bought the recommended Garmin hiking maps on microSD. Up until now, things have worked fine, but the latest update to the pre-installed maps has made life difficult.

I don't think it is unreasonable to be disappointed at the way things have worked out - thanks again for your help.