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.