Hello Paul,
Your mod is lookin' good! I suspect you should get 8+ hours of flying before you need to recharge the batteries. Nice job.
I emailed Christopher a couple of days ago with a question regarding the battery telemetry. He told me that the battery usage IS displayed in FreeFlightPro when connecting the positive and negative battery leads to the controller. He has a YouTube video verifying this. There is no need to connect the 3rd wire. Apparently, the blue wire (3rd wire) is not needed for the telemetry function. The only other thing I could think that this wire would be used for is the BMS part of the battery charging system.
So far the original battery pack from Parrot seems to be working fine in my SkyController, but if and when it fails I am going to do this mod. I plan on modifying the SkyController to allow charging without removing the batteries. It will be a little tricky but should not be too difficult. I'll do some bench testing before I actually mod the SkyController.
I know there are a lot of guys out there sending their Bebop 2's back to Parrot because of the battery problem with the SkyController 2P. In some cases, Parrot is sending them the old SkyController 2 as a replacement. I would much rather have the newer version SkyContoller. This problem is actually working to our benefit. The 18650 batteries are way cheaper than the battery pack provided by Parrot and the mod is simple. We are no longer dependent on Parrot for a proprietary battery pack. If we could (I feel eventually we will) work out a battery mod for the drone itself, we would be in great shape. Maybe someone will use a 3d printer and come up with some kind of carriage or sliding tray that would fit the drone. I know there is one available for the Bebop 1. I'll wait and see. (someone with a 3d printer please jump on this).
Please let us know how your mod is working and what kind of flight time you are getting on your twin 18650's. Take care, thanks again!