Brian, one of the greatest considerations when adding a redundant or backup battery is weight. By using the motor battery as the primary source one can use a very small backup receiver pack. The smallest I had was 800mAh but one could go even smaller. Most of us draw less than 100 mAh per flight so even a 300mAh pack would work. You might find that you could go to a larger motor pack with no additional weight if you went to this system. And I don't see why you couldn't use your existing Emcotec device. That is why I recommended just building an adapter cable because most folks already have the other components required.

Jim O