Car charger is not charging the device fast enough

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http://forum.xda-developers.com – Hi While I'm driving I'm using Waze for navigation, and the device is also connected to my in car multimedia unit via BT as a phone. I'm connecting the device to the car charger, and getting the charging icons, so it is actually charging the device. BUT... it seems that the charging is too slow. The percentages of the battery is going down, instead of going up. Yesterday while driving & charging, the battery totally got drained, and device turned itself OFF. The charger cable is Samsung OEM, purchased before for the Galaxy S2. I wonder if any other charger will better charge t (HowTos)