With my mains charger that came with my nexus 7 I can have the GPS on with maximum screen brightness and it still charges. Using a 1amp car charger although it showed "charging" it was not keeping up with demand so the battery would eventually run out. So I bought a 2amp car charger which improved the situation but still did not keep up with the demand. Although it was rated at 2amp it obviously was not delivering any where near the charge of the 2amp mains charger.
Can you please recommend a car charger that actually charges at the required rate. Thanks.