Duracell is a brand name, not the manufacturer. There is a Duracell company which makes disposable cells (alkaline AA's, for instance), but the lead-acid batteries are not made by them; Proctor & Gamble just makes deals to put their Duracell branding on lead-acid batteries made by other companies. Currently that appears to be
East Penn, one of the three or so big battery manufacturers (the others include Johnson Controls and Exide).
Like all of the battery companies, East Penn makes batteries of a range of quality and performance levels. Their main brand is Deka. I don't know where the Duracell-branded batteries sit in their range.