There are two common causes for this, that I have experienced: 1) the GTM25 charging unit had a badly assembled batch, that caused the outer braid of the charging cable (power return/ground) to touch the red +5V power conductor, that was stripped too far back to expose the copper wire, making it intermittently short. That does NOT blow the fuse, because the standard 5V regulator chip in the part that goes in the lighter socket, is designed to check for shorts, and just stop the 5V supply output electronically. The symptom is: the green LED goes out, and the Garmin will then not charge. The fix is to cut open the rubber part of the little “traffic FM receiver” part (the little slim black box), the one furthest away from the USB plug end, and insulate the bare copper wires so they do not touch, then cover the repair in more electrical tape. Ugly but it works. 2) the USB socket inside the Garmin has broken solder contacts. These CAN be soldered back, but you need a really good low-voltage miniature soldering iron to do this, AND it will need the motherboard removed, it is a major strip-down. I have done it, but then I use to install mainframe computers for a living .