Stop suggesting? I see it's your first post here, so I think nobody has suggested it to you.
Removing the battery and using a proper cable has worked for me and ~5-6 of my friends. What kind of cable are you using? If you check my earlier post, you'll notice that in my test, not all cables worked. GoPro original cable is fine as are e.g. UGreen cables on Aliexpress. All of my external batteries worked for me so my guess is that it's the cable that's the problem.
I think the camera uses both BT and wifi. Have you tried with different phones? The BT version changes between phones, so that might be and issue, too? I haven't had much problems with my Huawei Mate 20 Pro. Mate 10 Pro worked fine, too.
