I'm looking at two Napa batteries, but I can't quite figure out the actual construction difference aside from the obvious warranty difference.
Napa Legend 7559
(75 month warranty, group 59 size)
CCA: 590
CA: 700
Weight: 37 lbs.
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NBP7559_0398897352
Napa Legend Premium 8458
(84 month warranty, group 58 size)
CCA: 580
CA: 725
Weight: 28lbs.
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NBP8458_0398897353
They are different group sizes, but the dimensions are very close. I can't see where the nearly 10 lb. weight difference comes from. Both are normal lead acid batteries. I believe both are JCI batteries, as Napa carries Optima too.
I'm kind of leaning towards the 8458, but the 7559 has better availability.
Any thoughts on the weight difference?