Deep-cycle batteries, which are commonly used in RVs and marine vehicles, are sold at Costco under the Kirkland Signature brand. Costco has several different models of deep-cycle batteries available.
As with most products sold at Costco, the Kirkland brand of deep-cycle battery has near-replica versions on the wider market. According to the BatteryMart website, there are at least three models of deep-cycle batteries for sale similar to the Costco offering. It is a good idea to comparison shop before buying a new boat or RV battery. As of June 2015, Costco doesn't offer many accessories such as cases or chargers for its in-house brand of batteries.