Speak of the devil...my Kirkland battery (bought 11/2012, Mfg date 11/2012) died a few days ago. I replaced my Duralast Gold alternator a few months ago because it was acting flaky (while running, lights and gages would flicker), and I have to wonder if that did some damage to the battery. I went to Thailand on Dec. 10, returned on Dec. 21, drove the Explorer around town Dec 22-25 without issue, had a slow first crank/start on Dec. 26, and it dropped dead Dec. 27.
What I like about Costco is that they don't even have the equipment to test batteries, so there's no "we gotta put it on the tester" baloney. I got a replacement battery (Interstate, Mfg 12/2017) at Costco for $60 after tax and warranty credit for 40% of the price of the battery I brought in.