A lot of things can happen in 10 years to the boats, the owners and the batteries themselves. Being of a certain age I do not purchase "Green Bananas" anymore. I grew up with wet cell batteries and they have served me well over the years and they happen to be fairly inexpensive in today's times. I equate quality with the length and terms of the warranty and if I can get a guaranteed usage of a battery for two years I'm good and any additional life is gravy. I have had cheap batteries that just refused to die and expensive ones that died very shortly, no guarantees but those afforded by the warranties. A boat is mobile vehicle and a battery failure can and will happen a few hundred miles from where they were purchased and if the retailers do not have multiple locations with one close to where your mishap took place you may as well be out of luck. There is something to be said about Walmart batteries for the coastal cruiser, "you are cruising with a large stock of readily available spares wherever you are". Now that has value. We sometimes spend a few thousand dollars in an extended sailing trip and to incur in delays or missed reservations because you cannot find a certain type of battery to match your expensive bank would be a major inconvenience. I think every boat owner needs to decide which batteries to get according to his type of sailing and other circumstances. If there were 10 year batteries no one can say that your investing in them would be a wise decision all the time. If you want to know about the relationship between cost and performance of deep cycle batteries ask a Golf Car owner.