Currently have one marine starter and one marine deep cycle. Reading some comments here would I be better to replace with 2 deep cycle given how easy it is to turn over the etech 60?
Absolutely yes, this would be considered a "best practice"! The deep cycle batteries of this size range are more than sufficient to deliver the cranking amperage needed to start your E-tec. And they will take a lot more discharge cycles than a starting battery – so better for reliability and longevity.
Unless you are having some corrosion and gassing issues with your current flooded lead acid batteries (I haven't, and as Dave says, you shouldn't), there would be no reason to go to another technology. So far, no technology has beaten the standard deep cycle flooded lead acid battery for performance and longevity per dollar; (for example, a 50% greater price gets you much less than 50% increase in capacity). I've been keeping an eye on the technologies for a while now.
There are advantages to the other technologies, though, like; less “maintenance” (which means you don't add water... or can't add water if you needed to, which is not a good thing for long-term reliability); they won't spill (I haven't cracked a case or spilled a battery so far, though); freeze resistance (keep them charged and no battery will freeze); and less internal discharge (again, just charge occasionally when storing them and it won't matter), if you want to pay a premium to have those “advantages”. I don't – I have other things I'd rather spend the money on.
Again, if you buy a pair of batteries, ask the store if you can have two consecutive serial numbers. Battery construction in the factory varies in many ways as production progresses – you are more likely to get a good match this way.
Great idea about having the portable pack available, it will easily start the E-tec alone– they don't need much.