Make another connector out of stainless steel thread bar. Put a 6mm stainless steel nut underneath where the square terminal was. Screw the new stainles 6mm thread into the nut. Screw another nut on and tighten it up. Place battery cable back on and tighten with a new stainless steel 6mm nut. Now you have a connector that is easier to take the battery cable on and off. Using copper or brass washers in-between will also make a better connection.