http://www.rocketfishproducts.com/products/mobile-phones-gps/RF-PMC55.htmlI believe that this is the one that I have. The specs don't show its amperage output but it appears to be one in the same. The premium charger claims to charge phones faster. It does this by increasing its amperage output.
Best Buy carries this charger. You need to ensure that it has an output of 2 amps. This is the amperage necessary to charge the tablet properly. I bought mine a year or so ago for my phone. It claimed that it would charge phones faster than a 'normal' car charger.
Standard phone chargers have an output of .5 amps and will not trigger the N7 to indicate that it's charging. It may actually trickle charge the tablet if it is powered off. I haven't tested this on my N7 but it did work on another tablet of mine.
Anyways, any car charger that puts out 2 amps will work. Don't go into a store asking for a N7 car charger because you will most likely leave with nothing, or, the wrong one. They are out there, you just need to verify the output.
My charger also has a USB port so that I can charge another device at the same time. I plug my phone into that port via an extra cable. This allows me to tether my N7 to my phone and keep them both juiced up. I use Maps on the N7 and it looks so much better on he big screen!
