When I plug the USB in, the unit thinks it's plugged into a PC and goes into update mode. No charging takes place.
Are you sure its not charging? I use USB cords with both my Nuvi 5000 and 1350T from AC mains and in car. Both methods charge my GPSs, although the "PC connected" icon shows on the GPS display. The GPSs will also charge from USB when plugged into a PC. Leave plugged in for a couple of hours and then check your battery indicator.
However, please note, that the GPS unit will not work (Ie, you cannot navigate) when powered by a USB cable - at least my 2 won't.
The Nuvi's that I've seen all use a standard "miniUSB"(?) plug and that is the same one that the cell phone industry has agreed to use as a standard. here in the US, most of the USB chargers put out 500 milliamps at 5 volts, which is the maximum rating for USB devices.
You can go to any 7-11 or QuickMart (convenience stores) or WalGreen's (drug store) or anyplace that sells electronics, and buy a car charger with a miniUSB plug for $5-20. Most will be around $10, I'd avoid the really cheap ones but, they are here and they often do work. No doubt you have similar convenience stores over there? With racks of cell phone paraphenalia?
If you plug in a USB data cable and connect to your computer, the DATA LINES trigger the "PC connected" behavior. On a car charger, these lines are not connected, only the POWER LINES are in the USB plug, so the Nuvi will charge and run, and not go into "PC Conencted" mode. (There are four wires in a USB connection, two for power, two for data. The Nuvi knows the difference.)
I wasn't happy with the car chargers, so ended up getting a switching power supply, which you can plug in to 110 - 240 volt supply.
I have a Nuvi 760 and the charger works well. Leaves the Nuvi in standby mode when charging, which is around 30 minutes for a full charge.
Purchased it for around $10.
Hope this helps.
Well.. seeing the post of ross.bowden3 I did stay really interested in the idea, does that really approve? I do not have problems with the car charger, but if I have other option is always good to try... because I already saw many critics about the car charger that give me the idea that we can have better.