I took a peek under that red boot today.
I have never seen corrosion that bad.
It had eaten thru the bottom half of the cable terminal.
So I had to take the cables off the battery, pull the battery,
clean the posts and replace the postive cable terminal. Also put on
a pair of the felt terminal protectors.
So it's cleaned, repaired and greased.
I was fortunate to find something at Autozone that worked very nicely.
Damn 90 degree factory terminal.
But what would cause it to corrode so badly?
Could it be the cheap factory battery?

 

I think it is the factory cables mine did the same thing last year too and I cleaned mine alot to but it still got it,I have 07 4.0 too.

 

Man, last I checked mine it was clean, still original battery. Going to have to keep an eye on this.

 

Corrosion like that around the battery posts is usually indicative of a hairline fracture of the case-to-post. Whether it's battery acid or gasing, i'm not sure, but it'll cause corrosion. If it's still the OE MotorCrap battery, you're due for replacement anyway. I'm sure you've read all the battery threads.