[tphone]

Well, I admit it seems easier to carry the required charger, or have it available at all times.
But, I found myself traveling in New York and needing to use sprint navigation often. Without a car charger, after about 2 hours, you're done. I have a car charger in my own car so it's not an issue at home. And, had I known that Sprint Nav was such a battery killer and that I needed it, I would have brought mine. But, an extra battery would have been nice at the time. And I DO like the idea of an extra one being supplied with a separate charging system that can be very portable, unlike a charging base for the phone that just happens to have an extra slot for your second battery.