But then you have to rely on the car's data USB port supplying enough current to charge the phone while the audio + GPS are draining the battery. That's not always a sure bet, depending on the particular car's specs.
Other phones have separate ports for power and audio out, so they can charge from the cigarette lighter with more power while still playing audio and GPS through the speakers.
Does sending audio through a cable really take that much power that a USB-compliant port won't also charge at the same time? Sounds like a problem with the car, not with the port. Just because it's running over the same cable doesn't mean it's automatically half the bandwidth.
