Yeah, but I don't drive anywhere for a week or two at a time sometimes, so those ultra low capacity batteries would die very quickly. Kessy and all of the other constant on stuff would definitely make sure of that. Even with my agm, during winter when I don't drive for 4 weeks+ I have to hook up a battery tender.
If you can deal with those, then the minimum Brail I've found that meets the minimum CCA req (per vw) was 19 lbs i believe.
Isn't the factory battery 380 CCA? I found several with 480 to 680 CCA.