Check with Ford....batteries are usually pro rated, meaning they are warrantied for a length of time verses mileage. You may have a 4 year battery from the factory, so if it gave out early, they (your local Ford dealership) may give you a pro rating towards a new FoMoCo battery.
That's of course assuming you buy one from your dealership. I've always had great service with FoMoCo (Motorcraft) batteries. My 2005 F150 is on it's second Motorcraft battery; the first one carried me over 6 years.
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.