Its conference season and the same two things happen to me at EVERY conference.. First; at some point, the wifi will go down and normally JUST as I need it which makes iphone tethering a MUST and Second; my iphone will run out of battery.
I solve this by carring an extra battery... when I remember to take it with me... and remember to charge it. I know I can get a battery case, but they make the phone too big for me. So I got my hands on the sun-plugged iphone battery case and decided to give it a try. Its not dramatically smaller then any other case I have seen, but it crosses that line where it feels like a normal iphone case. And that makes a differnece. I used it all day and night during web 2.0 and I think I took it down only 50% and the iphone was still fully powered. Pretty good. Its $60 so pretty typical in price. I now have a new case for my iphone and no longer need to worry about remembering to take (much less keep charged) my spare battery.