Helo,
I m looking for an information: What is the dimension of DC plug of Osmo External Battery Extender?
ex. O.D. 5.5 mm  / I.D. 2.1 mm ??
I want to connect this extender with my portable Battery Power Pack with an DC and USB cable.
So? Anybody?

Unfortunately, there is not a great deal of information on this. Check out the specs section on the product page for any additional information on this point: http://www.dji.com/osmo/info#specs

I dont know the dimensions, but its the same plug as a standard Dell laptop power supply cable. I had plently lying about, chopped it off, soldered cables and away we go.