I have generic power bank made in China with 6 batteries model uses 18650 type battery.
It was fault, couldn't be used, couldn't be charged.
I opened the case, and found the problem.
It happened because the electric from battery didn't go to the circuit.
I looked for the reason, and found there was a broken component, it is like the fuse, or electric limiter.
The solution is: I take a small wire as new component and soldered it to change the function of broken component.
See the figure :
First I opened the case, remove all the Batteries, and take out the Board (PCB)
The broken component is showed in the red circle , click on the picture to enlarge. Its function is to limit the electric current.
Look for the small wire is not used around the house, smaller is better because it still have the function as a fuse, will burn if there is a short circuit. cut and solder it to the circuit.
Use electric soldering iron and small tin to solder it.
Wire is placed between B- and GND
Reinstall the Power bank, put circuit board back to the case, install the batteries carefully don't cross between positive and negative.
Now my power bank is back to normal.