The same happened to my X-T20, which I bought used just a couple months ago. Since it's wildly unreasonable to pay 90% of what I already paid, just for a battery replacement, I decided to just take it apart and see what's what, since it's basically dead, otherwise (everything resets in mine just when I turn it off and back on again with a fully charged removable battery still in it), I can't make it any less useful by totally killing it. Here's what I can tell you.
I'm no electronics tech, but I'm generally mechanically inclined. Only people who consider themselves somewhat skilled should make this attempt.
The case comes apart pretty easily by removing a dozen or so small philips screws. But the astounding design flaw is that the battery is on the inside of the main board, and to take that board out means unsoldering five wires and releasing five ribbon cables. That stuff is all very small, and delicate. I pulled it apart, and found the battery soldered to the board (why was this a good idea?) I unsoldered it and put two leads on it so I could wire a replacement battery that was easy to reach and replace in the future.
But I could never quite get it all back to working, when reassembled, and the more I tried to remedy the issues, the more issues I had. So mine is officially dead.
What's more upsetting than the series of design flaws is that Fujifilm wants to charge so much for the battery replacement. If I'd known exactly what I was doing, going in, and had proper tools and work space this whole thing would have been doable in an hour. So Fujifilm making this operation so incredibly expensive to repair adds insult to injury. Fujifilm should be apologizing that they sold a badly designed camera and replacing the battery for $50 (actually, they should replace it for free, it's their fault).
I'm considering selling my Fujifilm glass and buying something else, because I'm pretty angry that Fujifilm blew it on the design and then made it my problem.
Frazer
