So, I am late to this topic, but it finally happened to me. I tried every troubleshooting method I could and finally found what has appeared to be a consistent fix for MY issue. The issue is the same as mentioned, so this may help you, at least until a proper repair can be made. My batteries were not being recognized, so the boost mode would not work, and occasionally I would see the grip batteries indicators pop up for a second or two on my screen and then disappear. While checking all of the contacts I slowly unscrewed the grip tension wheel while the camera was still on. I found that the batteries would suddenly show up after about two full rotations. The contacts have apparently, over time, had some sort of short created by the constant pressure and now will lose contact if the grip is fully tightened down. I temporarily fixed this by putting some 1mm thick mounting tape down on the grip in a few spots, to fill the tiny gap created by not having the tension down fully (don't take off the plastic film, or your grip will be permanently fixed to the camera). Now, I can securely tighten the grip down to full tension, but still have that small gap, so there is not full pressure on the contacts. This is a bit of a ghetto fix and probably not a permanent solution, but now my batteries are consistently showing on screen and the boost mode function is working fine. I can barely see a bit of light between the grip and camera, so any weather sealing that was there is no longer, but at least I've identified the problem for my camera and maybe it will help you in a pinch until you can get it repaired.