what kind of car charger did you get?

[Tetegra]

I recently bought a mini car charger from walmart to pair my Lumia 920. During a recent road trip, I noticed that the charging rate just could't keep up with the battery usage rate of the gps and music play. The battery fell from 100% to only 30% after about 5 hours. I believe that the mini car charger is some kind of 2.1 or 1 amp. How big the charger should I get? 500ma, 750ma or 1A?

 

[EG8196]

I just use my old HTC card charger (HTC CC C300)
Amazon.com: HTC CC C300 Dual USB Car Charger with microUSB Cable: Cell Phones & Accessories