First set of three (blue top marine) still going strong (at ten years) in our previous boat. Currently have three group 31 (marine) in our present boat with three years on them and performance is as new. I'm totally sold on the spiral wound Optima line, but have heard of problems with some of the other more conventional AGMs. I particularly like the AGM service requirements (none) and their ability to be mounted at any angle, including on their side, etc. Everything on our boat was put together with the thought in mind that it might one day be upside down - the Optima's do that rather nicely (they are, after all, the number one battery used in the Baja 500 ). The Optima's do take a more aggressive charge and can be run flat without the kind of damage incurred in wet cells. We do not have refrigeration, water maker, etc and thus our needs are minimal, and this allows us to be on the hook for some time without recharging. We do have about 40 watts of solar which seems to be enough to keep us in the game. We also use a Freedom 20 charger which I am pleased with at the dock. If you intend to keep your boat for a while I think they cipher out money wise. They can be bought on-line for considerable savings by the way.