Total crapshoot. I've had OEM batteries last over a decade, or only a couple of years.
I had one Motorcraft battery in one of my old non-drivers last over 20 years. When I bought a new one last year and turned in the exchange, the counter guy couldn't even decode the little sticker to tell me exactly how old it was. I had bought it in the late 1990s when a buddy was a dealer parts counter jockey, and when I told him I finally had to replace the battery he sold me he was in total disbelief.
There are in some cases "hot" and "cold" batteries. I believe the colder ones have thinner/more plates to get a higher CCA whereas the hot ones have thicker/more durable plates with lower CCA. Like someone else said, out here in the land of the sun, batteries cook themselves pretty quick. If you can get 5 years, you are doing really good. That being said, we don't need much to start them in the winter.
My OEM battery lasted 2 years. My replacement battery, an Advance Auto Gold, is now 3 years old.
I've always had a policy of replacing batteries every 4 years. However Ford has put such a PUNY
battery in these cars that I will replace it this spring after 3 years regardless.
Mine died at 20k miles and 4 years. I should mention that I tend to work on the car a lot and have left it open isn’t our trickle being plugged in or attached. So that will kill ya fast.
My stock battery did not make it 5 years/20K miles. Kept in an insulated garage with a CTEK charger on it. The cell closest to the negative terminal is reading bad. Trying to revive it right now with a BatteryMinder charger but not looking good.
I put in an Optima 3478DT Red Top since the price was right (free). Had a do a lot of custom work since the posts were backwards. Plus the battery cover does not fit (too tall). Not sure if this an issue or not since my other vehicles do not have covers.
Would like to go back to a stock size battery. A few options out there. The Odyssey 96R-600 looks nice but not sure I want to spend $250 for one.
Most modern cars will get 5 years tops in a normal climate, less if you live somewhere that's perpetually hot. I just swap at the 4 year mark from the build date, never had a failed battery from doing this.