First issue are the new four strokes, they require more CCA then a 2 stroke, so there really are no deep cycles that will start them, and if you have one that just covers it, to use that power your putting a big strain on the engine, deep cycles can handle deep discharges over time, not quick rapid ones well, so each turn of the key hurts those plates and will wear them down over time, similar to what happens from a deep slow discharge on a starting battery, advantage a starting battery has is even with the electrical discharge for electronics over time, a typical user who drifts will move every half hour where they can rapidly be charged back to full and are charged properly for that type of battery, and starting it has no effect on the battery. Only problem a starting battery would have is for guys who sit for long periods of time, they might draw batteries lower, but no reason that if you know your gonna be anchored a while you cant switch to one of your 2 batteries to ensure you have one to start, we all have a spare battery since the house banks have 2, and if we don't should add one. If it gets low start the engine off both, charge both up again for 10-15 and then switch back, will never not be able to start. either battery is not the best choice, but Yamaha limits us with their charging systems style of charging. A dual purpose would be a far better choice then a deep cycle, I would not use a deep cycle at all.