Exactly, the factory terminals can suck, they do not have the range of tightening the after market ones do. Once you clean terminal ID with a battery brush they often let terminal slip by hand force even when as tight as they can get. Been there on two Foci. Replacing just the terminal can work for many years if one is competent. I custom made my battery cables from bigger cable after the Ford ones melted on both cars. They've now lasted longer than the Ford ones did.........one is over 10 years old and still works great. The Ford factory battery cables suck quite frankly to me...............
I toss that spiffy looking plastic battery cover lickety-split too, it only retains heat in and around the cable's first few inches, where it then begins to melt in hotter climates.