12-24v Run off 3s to 5s.
This was my first one, I made a much nicer one but I lost it, just ordered some more to try again.
I use em when I'm travelling to charge phones, sat navs, ipads. 5000mah 4S lasted me + wife over a week charging all our usb gear.
I know hobbyking made one but it was restricted to 2s and didn't seem to do the full 3amps which you need if you are charging an ipad.
(http://i.imgur.com/qje7nOi.jpg)
Have you got a link for this please.
Nice :) I did the same concept using a Bec last year for work. Bit bulky carrying a 5000 mah 3S around but a life saver on a night shift when your out in the sticks :)
Something similar to this? http://www.ebay.co.uk/itm/12V-to-24V-DC-2000mA-Dual-Twin-2-Way-USB-2-0-IN-Car-Power-Charger-Socket-Adapter-/350950256297?pt=LH_DefaultDomain_3&var=&hash=item51b643eea9 (http://www.ebay.co.uk/itm/12V-to-24V-DC-2000mA-Dual-Twin-2-Way-USB-2-0-IN-Car-Power-Charger-Socket-Adapter-/350950256297?pt=LH_DefaultDomain_3&var=&hash=item51b643eea9) nice idea! *Clicky fingers order a couple*
-Al
or this:
http://www.ebay.co.uk/itm/3-1A-Dual-Port-USB-Car-Charger-for-iPad-iPhone-3G-4S-HTC-Samsung-P1000-TomTom-UK-/121281723446?pt=UK_MobilePhones_MobilePhoneAccessories_MobilePhoneChargers&hash=item1c3cf43c36 (http://www.ebay.co.uk/itm/3-1A-Dual-Port-USB-Car-Charger-for-iPad-iPhone-3G-4S-HTC-Samsung-P1000-TomTom-UK-/121281723446?pt=UK_MobilePhones_MobilePhoneAccessories_MobilePhoneChargers&hash=item1c3cf43c36)
Pretty much any in-car 12-24v charger will do. There are lots of em about on eBay. They are just a cheap mass produced 5v voltage regulator with on board USB ports.