Ok so this is how bored I am sitting here waiting for my girlfriend. It would take approximately 1.5 hours to charge and iPhone 4 from a car charger from 0% with no phone calls, texts, or alerts, and with the phone in standby. No I didn't let my phone die and wait that long. Here's what I did. I wrote down then percent I was at and start time that I started charging it. I let it charge for 5 minutes. At the end of the 5 minutes I wrote down what the end charge was. It was a 3% difference. So 3% in 5 minutes. So it would take 166 minutes or about 2.7 hours to fully charge an iPhone 4 on a car charger from 0%. Any math wiz out there want to check that to see if I'm right?