" Now, they go bad in 3-4 years."
My experience with automotive batteries is the opposite.
Early VW diesel Rabbits would trash a battery in three years. Their glow plug circuits were not very efficient and unless you were packing on the miles, in cold weather they couldn't handle the drain.
I think I replaced the battery once in my '93 Passat turbo diesel, before I traded it in '07. I anticipate changing the battery in the '06 TDi in a year or so.
Same story with the '96 F150. It didn't get used much in the winter time but the frame rusted out and the dome gasket failed but the battery was still rolling the engine over.
Best
Les