I made myself a custom car dock for my GS3 so I could use my Titan Kraken case modified to take an extended battery. The setup works great, but I've noticed something very strange. I have an NFC tag in the dock to launch Carhome Ultra. I was noticing that on my 30 drive home from work, my battery (which is charging in the new dock) would discharge about 2%. I was using a generic micro USB cable plugged into my Ravpower DC adapter, which maxes out at 2.1 amps, which is plenty. As an experiment, yesterday on the way home, the first 15 minutes I had the generic cable plugged in. After it dropped a percentage point, I unplugged the generic cable and plugged in a cable I got with a Mophie that I had. The last 15 minutes of the trip it went up 2 percentage points. Keep in mind, same DC adapter, same phone & battery and same apps running. Can anyone explain why this is? I have experienced the same drop with at least 2 other cables. The Mophie cable and one other that I have will 'keep up' with the power demands and actually charge the battery too. Just wondering what I should look for when buying USB cables in the future.