I noticed a common theme , buy a charger that is spring loaded so you dont find yourself cranking down on it when the light doesn't flash red due to ejuice between the contact surfaces. Clean it, clean both! The spring loaded kinds have a nice center button with a good spring to add the force between the contact surfaces. You prolly stripped your threads, it doesnt have to be tight like a pipe.
Or buy a multi charger spring loaded:
Ebay item number 201110786197