Hi, I'm a heavy user of my MacBook Air 2013 (i7 1.7 GHZ, 8 gig RAM, 256 GB SSD). I use VMware on a daily basis for virtualization, listen to music, view videos, and utilize XCode. I normally pull 9 to 14 hours out of my battery based on what I am doing. I am considering purchasing a 128 GB SDXC card for time machine backups, since I currently don't have the funs for the large external HDD I need. Plugging in my external drive has become much more of a hastle these days, especially when I'm away or out of town; It's a 2009-2010 500 GB desktop drive, heavy and metal. My question is: how much would an average SDXC card cost in power if I left it plugged in all the time? Would loss be so exponential that I would have to begin unplugging it? Is there some sort of power saving feature for SD management? Thanks in advance.