Makes sure that the charger will work with Nano 3G. I have had the same problems with charging away from the PC. My iRiver never had a problem with with either the car or mains USB charger I have but the Nano will not recognise the charger. I does work with the powered hub I have and this makes me wonder if somehow the nano needs to see some residual power source on pins 2/3 of the connection before it will charge.
I really don't understand why Apple have done this but it's a sorry introduction to their products for me, especially with regard to compatability.