Actually I have been interested in this for some time and I just tested it out. I have a Samsung Galaxy Tab Pro 12.2 and a Seagate 2TB Slim. When watching video from my internal 128GB SD, I lose about 1% power ever 10 minutes, mostly to the screen I assume. I formatted the Seagate as exFAT and loaded some videos, then connected to the Samsung via OTG. Mounted no problem. Playing video from the Seagate external hard drive drops the battery about 1% per 5 minutes. Now that may sound like a lot, but that means with a full charge you could get about 8 hours without a re-recharge or external power. I could preplan what I want to watch on a long trip and place it on my 128GB SD, or I could take my entire 24TB collection of movies and TV series with me on the 12 Seagate 2tb Slims I use to backup my media server, which are relatively small and light, and not be restricted.