Had to make an account just to post on this thread. I have had the same issue since purchasing my X-T2 in June 2017 at a store here in Ottawa, Canada (camera + grip + 3 official 126S batteries in total). Not that it matters, but this was my first pro digital camera. Did a ton of research, saved up for months, and was tremendously excited.
The confusing sight of both grip batteries registering as dead, when I knew they were fully charged, happened the very first time I used the grip. After noticing this a few more times over the following weeks, I sent the grip in for repairs (Fujifilm Canada near Toronto). When I received it back 6 weeks later I was told there was nothing wrong with it. Within minutes of testing it out of the package the issue re-appeared... I remember feeling pretty crushed.
I haven't been able to consistently replicate the problem, but seems the combination of CH and AF-C, with the grip set to BOOST (a setup that's the very reason to own the grip) almost guarantees it. However I largely suspect it's a connectivity issue between the grip and the body, not a shooting settings issue. Different levels of tightening give different chances of it happening, where the tighter = the more likely. I should point out that, as others have mentioned, the camera works absolutely flawlessly without the grip, and I would bet my life on the X-T2 otherwise. But it doesn't feel like the same machine when I put the grip on.
Last spring, nearing the end of my warranty, I decided to sent both the camera and the grip in once more. This time I even included a thumb drive with 2 videos of the issue occurring.
After receiving and testing it, Fuji emailed me to say there appeared to be no issue with either item. They acknowledged my videos but were not able to replicate the issue. This was puzzling to me. I called a rep and pressed them on this, I told them I had had the issue consistently since day one, and what happens when they send me the camera back and this keeps on happening? How can I trust it? How do we solve this?
To ease my concerns, the lab agreed to replace the camera's main board as a solution. I appreciated they were going out of their way to help me with this. However when I got my camera and grip back, with a new main board, the issue quickly re-appeared. I have felt rather helpless since.
I have shot my niece's soccer games, pet portraits, friends' softball games, and a Formula 1 race among others -- situations where boost mode and AF-C are exactly why I paid more than an X-T20 -- and each time the red batteries would make an appearance, making me doubt this pro-grade camera. Reading all these accounts of similar issue and realizing that Fuji must know it's a problem but doesn't acknowledge it is making me pretty upset. I had heard they're supposed to have great service, instead now I feel like they're ignoring or covering up a known manufacturer problem.
I will keep checking this thread for any fixes in the future.
