I would try to isolate the problem by probing some other functions. Like, what happens if you plug a battery that's fully charged and only connect to the PS4 via bluetooth? If the controller works fine like that, I would then move to the flex cable and USB board. Are they in good condition? If so, the next would be checking the USB cable itself and the USB port on the PS4.
If the problem still persists, I would start worrying about the board itself. We know that the vibrators are not to blame because you already removed them. So what about the touchpad? Does removing the touchpad do anything? If the problem still persists, the next would be to check the temperature of the charge IC and CPU. One time I also had a JDM-040 that would do all sorts of crazy stuff because of an inductor that had been knocked off the board near the charge IC.
If you still have the problem, you can update with the details of everything you tried by then.
