Should be H5 480CCA or H6 570CCA for best performance.
Costco does not have all the groups sizes, if you own a Hyundai which requires Group 121R you're out of luck so it might be the same with Group H5 or H6.
Also check the date code label on top of the battery, most stores don't rotate their stock, buy one that says 11/17 or 12/17 and don't bother with ones that have 6/17 or earlier or you will be buying a defective battery to start with.
Costco does not have all the groups sizes, if you own a Hyundai which requires Group 121R you're out of luck so it might be the same with Group H5 or H6.
Also check the date code label on top of the battery, most stores don't rotate their stock, buy one that says 11/17 or 12/17 and don't bother with ones that have 6/17 or earlier or you will be buying a defective battery to start with.