My factory battery died after the car sat for about 2-3 months as it was almost 3 years old. This was normal behavior from what I had seen as a Ford Service Writer in my days doing that.
Got it replaced under warranty. The replacement has been going great ever since. I did add a battery tender at about the same time as getting that new battery, so I'm sure it helps.
And in my Advisor days, I sold many Ford 100-month-warranty batteries (they have other, cheaper ones), and almost never had an issue. For some weird reason it seems that the batteries we sold over the counter (same stuff we'd use for warranty replacements) would last much longer than the batteries installed at the factory.
Motorcraft is one of the best batteries out there based on experience and research.
What he ^^^^ said.
Just fyi Motorcraft batteries aren't made by Ford. Thiers only like 4 companies in the world now that makes batteries.
The same company that makes diehard , interstate batteries makes motorcraft.
Yes, only a few companies, but I'm sure they build different brands to different quality levels.
On a side note, the new Interstate battery I installed in my Tundra at the end of 2014 is still going strong, truck spins up fast and strong every time, even recently when it sat for almost 2 weeks while the wife was sick and I was driving the new VW wagon around for errands and such.
And yes, Optima batteries have earned a shit reputation recently, I'd stay away.