I've been a mechanic for 15…
I've been a mechanic for 15 years. If you don't buy the cheapest batteries you can find, they last 5-7 years. If you're replacing them after 3 years or a mileage, you're doing something very wrong.
Also I can tell you're buying crap batteries, cause all the ones I put in are 3 years free replacement, and then prorated after that. So if I replaced them every 3 years, I'd never make a dime after the first one.
I'd bet money this is an AGM battery, with high CCA. Which is why its so expensive.
You see them a lot in the newer jeeps, they'll have a small AGM under the passengers seat. And they're very expensive.
Stop going to the dealer. Avoid shops that pay their mechanics flat rate. (Which is every dealership). It makes mechanics want to cut corners to do the job faster, they'll skip problems that are not quick fixes if they aren't a good money maker for them, and they'll try and sell you extras at all costs. Avoid flat rate and dealerships.