Garmin GPS stops working

Have you checked the fuse in the cigarette lighter part? I have similar and it is always plugged in through the cig lighter power supply, only turns off when I turn the ignition off but warns me and I switch to battery. Either that or there is a problem with the lead?

I recall that the warranty on Garmins sold by GME have a 2-yr warranty in Aust. With this technology, there's not much you can do to fix these things outside a properly set up test facility.

I can sympathise - I still have an old GPS2+, and decided to update the internal software, carefully following the instructions. All was going well, as the screen indicated first software connection update, deleting data, then "comms failure". That was it! From then it wouldn't talk, and neither could GME get it to talk. And it was out of warranty. In the end, they offered me a re-furb unit with later software for about half what I paid for the original. So I still have it but as a backup.
Gerry

The thing with Garmin and their batteries is annoying. I have a garmin GP72. After a lot of mucking about, similar to your story, in the end, I discovered the issue is that the batteries have to be properly connected.
When I plug into the 12V, it sometimes worked, or not. The batteries get loose, and the unit will switch off, even though it's plugged into the 12V. I discovered this whilst off-road, and with all the bumping about, the batteries got loose in their cage, and the unit stopped working.
I solved the problem, by simply opening the cover for the batteries, folded a thin sheet of cardboard a couple of times, and shoved it in over the batteries, and under the cover lid, and snapped it back in, to hold the batteries firmly in place.
Never had a problem since.
So much for manufacturer designs.