why doesnt the 4 gen ipod nano charge on certain chargers that work perfectly fine with all other previous generations?

i have a 2 gen ipod nano that would charge in my wall socket charger and the car adapter i got for christmas. My dad has a 3rd gen nano that also works with said chargers. But why wont the 4th generation work with these chargers? it simply says on the screen "charging is not supported with this accessory"

gus13328 years ago
With ipod nanao 4th gen Ipod touch 2nd Gen and ipod classic 120gb will not charge on normal chargers. To charge without a computer they require about a 2V load on the D+ and D- Pins in the usb connection. This can be done with a few resistors.

5v---|-----100k-----|----20k-----|----100k----|-----0v

This is shown on the site http://www.tzywen.com/modules.php?name=News&file=article&sid=683

I think the best option for you would be to modify a usb extension cable.