I have a macbook air 13" 2012. battery life is not what it used to be. it's telling me to serviced my battery. its only up to 67% of the original capacity and I can only watch a movie on medium brightness for 2 hours and 30 minutes. i like to watch 1 movie when I fly in an airplane. of course i want to conserve as much battery life as possible during the flight to finish the movie, but i am running out of computer memory space. i'm thinking of moving the movie files to an external hd or sdhc card. i own a small external harddrive, seagate passport. will the battery drain faster if my computer is connected to the external hard drive when watching a movie? (i dont have much space in my mba). or am i better off transferring the movie files to an SDHC memory card? any advice is appreciated.