And to add to Edward's great info, the yellow top and blue top are internally the same chemistry, when the cases are the same color. There is a light gray case that is a traditional deep cycle, and then the charcoal case, which is deep cycle/starting combined. And of course the posts on the blue top give you more options, as Ed said. I'm loving my dual yellow tops so far, although aside from starting the oil burner, I have really not put them to the test yet.

1991 HZJ77, 1999 KZJ90, 1999 UZJ100, 1992 M101CDN2
https://www.thegearheadproject.com/category/jdm-journeys/