All, I am looking into buying a new Macbook Air and use my Macbook Pro as my home desktop. I am on the road alot and needed a lighter option since my work computer is useless for personal use. I wanted to get the base 13' model and use a portable hard drive to keep my music, photos, movies, etc. I know the default stuff takes a good 10-20 GB off of my space which would leave me with about 100 GB to spare. How much affect does the battery life have on using the portable hard drive. 30%, 40%? Just would like an idea of how much juice it zips from the battery. If its not that much, I might downgrade for an 11 inch. Thanks for your help. I was trying to save the $300 bucks and not get the 256 GB model if possible.