Charging an iPod from 12V in a car

[TTL]

I recently found out that my car-stereo has an external audio input option, and this would be perfect for bringing my iPod (iPod Touch 4th generation) along. Audio should be no problem as I have the pinouts for the car stereo from its manual, and I found the iPod pinouts here. I could use the dock connector for that, and while I'm at it I'm hoping I can also provide charging power via the dock connector as well, but how?

Normally, the iPod is charged via USB, which I believe is +5V and GND, but what do I need to do in order to charge from +12V? I assume I also need to limit the current for a normal charge (I don't want to put excessive strain on the iPod battery).

 

[Bluejets]

Must be millions of 12 to 5 volt auto converters out there in Ebay.
Plug into the aux power socket in the dash( previously the cigarette lighter socket)
Already provided with a usb socket.

 

[Chemelec]

Not sure Where you live, But DOLLAR STORES have Many of these USB Adapters.

 

[Kiwi]

Suggest get an adapter with at least 2.1A(2100mA).

 

[TTL]

Good suggestion although the cigarette lighter is already occupied for a GPS so I'll have to plug it into the +12V/GND connectors on the back of the car-stereo.
Regarding amperage: is it correct that a higher amperage will charge the iPod battery faster (but also put more strain on it and thereby shorten its life) and likewise a lower amperage will charge slower but also treat the battery more gently? I'd prefer the latter as power will be fed into the iPod constantly anyway, so how many Amps should I go for?

 

[Kiwi]

The regulator inside the iPod will limit the charge current to a safe rate that doesn't shorten the battery life.

Using a higher rated charger/adapter will probably allow for faster charging. Depends on the size of the original charger.