I wish these 5v USB batteries were around and cheap back in the JB3 days! Back then, I had a Marc Kim aka Leegeddy "Voltage Regulator Box" that took a 12v or 9v or 6v power source[can't remember] like an SLA[this was 2004-2006 mind you, so this was SLAs were still cheapest and most reliable power back then], and its stepped down the voltage to 5v for the JB3! That way, from one battery, I could power BOTH my V3@6v/9v/12v, and the JB3@5v, since it had dual outputs! I could've run a MUCH smaller USB battery for my JB3 and my v3 from the 6v SLA, but that would make two separate batteries
Still much smaller than the HUGE 12v SLA that I had for Phish Summer Tour 2004, which would power my v3 AND JB3 for like 24+ hrs straight
Anyway, I just ordered this cable from China, so that I can power my 70D's from  5v USB batteries at once! This way, I can get over 20+ hours straight, from 2 of my USB batteries, powering the 70d with all 4 channels@24/96,Phantom on 1/2 and Line on 3/4! That's pretty badass IMO http://www.ebay.com/itm/172151661611?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
I run this Left Angle Micro USB>Right/Left Angle USB A cable, from my 70d>directly into the above USB cable splitter!
Works GREAT so far! I'll probably pick up another one or two of those USB splitters above, since they're sooooo damn cheap http://www.ebay.com/itm/381090437511?_trksid=p2057872.m2749.l2649&var=650404631055&ssPageName=STRK%3AMEBIDX%3AIT