I've given this a lot of thought back when the traditional flooded batteries kept dying in the 2.0T cars - those don't even have stop/start and were croaking at a year or two. If you search around the Google, failure in 3-5 years seems the norm now across all manufacturers. I've wondered if it is indeed new batteries are just junk. Lots of reasons to suggest that as the reality - collapse of North American battery production, cost cutting/greed, lack of component engineers etc. But I've also considered whether it is coincidence with the proliferation of demand on those batteries in cars. In the last 15 years typical demands have grown from an ECM, starting, and power windows to always on 7-10" infotainment screens, always on OnStar modules for remote connectivity, 4G wifi routers, dozens of modules/sensors for airbags and engine operation, proximity sensors, not to mention the wear from stop/start systems on top of that.Today's batteries a junk.
Great way to look at it to be truthful! Our new cars are so computerized that there is a ton more load on the battery. Think about the high speed LAN connections and other things that are constantly being powered. Even my Impala knows as soon as I remote start it, what temperature it is outside and whether heat or A/C should be used. Let's face it, our cars do a lot more than just keeping the time and radio stations preset while sitting. Now our cars are almost like they're in standby mode, ready to go at a moment's notice. Almost nothing is mechanical on a car anymore that doesn't have a computer commanding it.If the old standard was 5-7 years and new reality is 3-5, regardless of the cause (junk batteries vs more stress/demand), it seems 4 years is the time battery replacement should be considered as maintenance.
Then add the southwest summer heat and the extra heat from the 2.0L turbo next to the battery and you have a 2 year replacement cycle, AGM or flooded (good time to get the Walmart with the 3 yr replacement warranty).Highway miles are almost always kinder on vehicles than city.
Heat kills batteries faster than cold, but cold is what puts a bigger strain on them when starting due to the reduced CCA available and the slightly stiffer engine that doesn't want to turn over so easily.