Ordinary staring batteries are not SPECIFICALLY DESIGNED to be deeply discharged and recharged repeatedly. Deep cycles (DC) batteries are. Its not a difficult concept.
You should stop trying to justify your mistaken statement that a DC battery is required for Mazda iStop vehicles.
Yes, you can use a DC battery to start a engine and it works. You can also use a starting battery to run fridges, electric tolling motors etc where significant discharge/recharge cycles happen regularly.
But neither will perform as well or as long in their unintended role, as how they will perform if used for the purposes for which they are designed and intended. And DC batteries are usually more expensive than a similarly specced starting battery, so it doesnt make economic sense to use one as a starting battery either.
I have used both battery types extensively for 40 odd years in the boating/marine environment, so I do speak on the topic with some level of pratcical experience, not just theory.
I use a deep cycle 120ah battery on my river boat to power my bow mount electric outboard, because that is what gives it the most useful run time and because the deep cycle is DESIGNED TO and will tolerate the 40-50% discharge and recharge cycles this type of use involves. It will outlast and outperform a normal car starting battery performing such a role by a large factor. Been there, done that.
I use a high cca starting battery to start my outboard motor, because thats what it requires to fire the efi system up. So one boat, 2 batteries, each assigned to their appropriate role, for optimum performance, battery life and $ value of both.
That is why there are two types of batteries, each designed to be used for different purposes. One for starting, one for prolonged power output. If they were the same or were truly interchangeable like you seem to want to argue, why would there be batteries designated as starting or deep cycle available?? It makes no sense.
AGM simply describes the battery construction. Despite what youve been told or googled, there are both AGM starting batteries and AGM deep cycle batteries. Just because a battery is AGM construction, doesnt mean that its also a deep cycle battery.
So, to get back to what started this debate and deal with the facts:
1. You are incorrect. IStop does not require a deep cycle battery.
2. The Mazda iStop system is designed not to put extra strain on anything, not even the starter motor. Google how it actually works and you will discover the facts. Here is a start for you - read the whole lot, and view the video, and you will discover interesting facts as opposed to assumption and rumour about what is involved.
http://discoveryourmazda.com.au/mazda-istop-explained/
I trust that this info assists your knowledge of batteries and iStop.
Now, your turn to educate me - What is this reference to a "fluid filled engine support" that iStop supposedly puts strain on? Can you provide some References from Mazda that explians it please?