I think maybe my thread was missunderstood, let me explain:
First, for those of you that may have read my threads in the past, I am a VERY STRONG ADVOCATE for a seperate, independant, out of the loop, starting battery. Period. If I am not mistaken, to meet ABYC, you MUST have it seperate. I think many manufacturers get around this by putting in a 1/2/both switch so that in theory one battery is a starter... whatever. Terrible setup. Terrible. And for those of you that are still doing what I did for many, many years (like switching your batts between 1 & 2 on even/odd days), you better read a few books about electricity. You exponentially (not linear) reduce the life of both batteries. Very bad idea. Go read Nigel Calders Boatowners Mechanical & ELectrical Manual, talk to a battery manufacturer, or any electrical engineer. Parallel is much, much better and will vastly extend the life of boat batteries. I guess the exception is if you do not have a starter battery... but I don't think I need to cover that ground again.
Now, my statment:
Deep cycle cells are built with heavier, thicker plates versus a typical start battery is built with a typical thin plate. We tend to (as cruisers) associate a thin plated battery as bad and a thick plated battery as good. This may not be the case at all. When you start your engines, there is a huge, but short (hopefully), amp draw which pulls the juice off the surface of the plates... but that is it. This can then be easily replenished with a quick charge. A deep cycle battery would also pull the surface charge off but then get deeper into the plate, requiring what we often assocaite with as needing a multi-state charge to replenish the "interior" of the battery, not just the surface.
Yes, you can use a deep cycle... but the questions is, perhaps it really is not the best battery for that purpose (not to mention the cost)? Could the argument be made then, to use a true, NON deep cycle battery?? I would say it could. My logic off anywhere here?