I need an additional source of power for my computer. It is a toss up between either the Air/Auto adaptor or an extra battery for my iBook. I am not sure which to get. I see the benifits of the battery is that it is less hassle to carry (a tiny square versus all the cables) and I can use later on if my primary battery starts going. The downside is that it is about $30 more and my time is limited to the length of two batteries. The adaptor is cheaper and provides unlimited power while I am in a car. I say only a car, because the last time I took a cross country trip on a plane the seats were not equiped to plug into. I am wondering if I should just get the auto/air adapter or should I get the extra battery and then later on get a $30 adapter for the car (I read somewhere on the forums of someone doing this). Thanks!