We installed three Costco new deep cycle batteries when we bought our Beneteau First 310. We followed advice to simply disconnect them over the winter and it seemed to work o.k. Howver, the following year we replaced our starting battery from a local battery shop; and they strongly advised leaving batteries all connected with periodic charging over the winter. Since they only sell batteries, we follow their advice. They tell us that boaters that don’t have access to winter yard power should remove and periodically charge the batteries at home.