So I didn't go through all 20 pages of this thread to see, maybe it's been answered already. What's the cost of this mod to add 6 extra minutes flight time?
The cost really varies. If you already own a LiPo/LiHv charger then all you need are the external batteries, a good one costs around $22. The mod is available for I believe $40 + shipping. You could also make your own pretty easily with some simple tools. The strong lock Velcro is around $4. The 3D printed mount is not a necessity but if your worried about the batteries falling off isn't a bad idea. The controller mod is a completely different story though. I have done some more tests with LiHv and I still believe using two on either side of the Mavic is best, now my new results with those is around 6.3 min on sport mode which to me is an amazing amount of time. It's up to you if you feel it is worth it or not, but for me those extra minutes can be the difference from a failed shoot to a successful one.