Hi Colin,
As in my previous post, I am not yet very knowledgeable on this Mazda, but I have driven "mild hybrid" vehicles for a while, and this is what I have worked out so far (please any real expert chime in and correct me where I have worked it out wrong!)...
A vehicle can be claimed to be a "mild hybrid" if the alternator has a clutch, which does the following 3 things:
1. Disengages during normal driving unless the battery needs a top-up, to reduce load on the engine and so (marginally) save fuel;
2. Engages at any time that the battery needs a top-up, so as to keep it charged;
3. Engages during braking / deceleration in order to provide some "drag" on the engine (help the deceleration & reduce brake friction / wear) and also to utilise ("recover") some of the energy - that would otherwise be lost to heat in the brakes - to charge the battery (and so not use any fuel in this charging, providing further marginal savings).
Cars that only have the first two of these are said to have "smart alternators", but cars with all three can claim to be mild hybrids.
Now mild hybrids can use any battery system they like, and typically can operate with their normal 12V battery or they can be 24V (as the Mazda), or 48V as in newer designs from VW, Volvo etc).
For a car to be a "proper" hybrid there should be some active engine-assist from the electrical source (e.g. Toyota hybrids) but the various flavours of mild hybrids can provide any benefit from "just providing free battery charging" through to specifically operating the starter and pushing the engine into rev-matching during gear changes etc.
Some manufacturers barely (if at all) make any fuss about these systems, particularly the 12V ones, it is just one more little thing they do to meet the ever-tightening efficiency requirements (lead by EU). For example, my 2017 Audi has an instantaneous fuel-use indicator on the dash, which moves below zero and turns green under braking. This is the only indication that it is a "mild hybrid". Very mild, it is just telling me it has engaged the alternator clutch which is charging the battery with energy from deceleration and so providing an instantaneous "negative" fuel use.
The CX-30 (with X 20 engine) uses the Mazda M-Hybrid system which does the following:
1. There is an integrated starter generator connected to a 24V Lithium battery. This is belt driven and has a clutch so as to only engage when needed. There is no 12V alternator nor starter motor as far as I know..
2. The clutch on this device operates as I described in the list at the top of this long post when the car is going, it also engages to act as a starter motor (cold starts and i-stop functions), and as engine assist in limited other cases (rev-matching in MT gear changes are described somewhere).
3. There is a 24V/12V DC-DC converter. This provides charge to the regular 12V battery, as-needed, from the 24V lithium battery. Note that the 24V battery will always have enough power for this as it is not only charged by regenerative braking but also when the computer decides that the voltage is a bit low and it needs a top-up. If you want reassurance about this then watch the energy flow display during normal driving and you will see this combined flow from the engine to the front wheels and also through the displayed clutch to the battery from time to time (in my experience, only when the lithium battery shows 2 bars or less of charge).
Sorry for the very long-winded description, but this is why I asked my original question in my first post, and why I don't think the CCA are too important in the 12V battery, as long it has enough energy storage (Ah) to be able to turn on all of the systems necessary to instruct the 24V system to start the car!
Hope this helps in some small way.
As a reference for you regarding the 12V battery, here is a photo showing the rating details of mine (55Ah, 335 CCA), Japan-built CX-30 X-20 engine (Oz spec).
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