Ipad won't charge in car...

Hello, I got the new ipad with cellular. Now the charger that I received with my ipad supplies 2.4A, which is sufficient for it also when I'm using it extensively. However, the Griffin PowerJolt car charger that I bought from apple store supplies only 2.1A...so when I'm using the ipad extensively in the car, it does not charge and even worse - drops my ipad battery to lower charging percentage (though in a slower rate).

Now I haven't seen any 2.4A car charger in apple store, the only one that I've seen is 2.1A charger, and I am reluctant to buy 3rd party non authorised car charger so as not to harm my ipad.

Your help will be appreciated. Thanks.