This is from www.consumerreports.org about car batteries:

Who makes which brands for whom. Most automotive batteries are made by just three manufacturers.

Delphi makes ACDelco and some EverStart (Wal-Mart) models.

Exide makes Champion, Exide, Napa, and some EverStart batteries.

Johnson Controls Industries makes Diehard (Sears), Duralast (AutoZone), Interstate, Kirkland (Costco), Motorcraft (Ford), and some EverStarts.