I noticed recently that with my iPhone 3GS plugged into my car stereo (a Pioneer unit with USB) it charges, but not very well. If I'm running Navigon and playing music, it seems that the charge just holds steady instead of increasing. I thought this was normal because the GPS app needs a lot of juice, although I wasn't too happy. Yesterday I was using Navigon in my brother's car who only has a tape casette adaptor and a Belkin cigarette lighter charger. We were using Navigon and playing music. Much to my surprise, the charger charged my phone up to 100% very quickly even with the GPS being used for about an hour along with music. I've gotten used to the fact that my stereo would simply hold my battery steady, or increase it a few percent while using Navigon (if it's just playing music, it charges faster). But either way it seems the cigarette lighter charger is better/faster at charging than my Pioneer head unit with a USB plug. Is this to be expected? Or is there something wrong with my Pioneer stereo?