Yeah - in all my BMWs (most recently the M235i), both charger cables I always attached to special terminals under the bonnet rather than the battery posts - but then, as we all know, the battery is the back in those cars.
I found this to better explain what happens. https://www.mazda.com/en/innovation/technology/env/i-stop/
I thought I should add that if I sound like Iām missing the base idea of engine stop/starting at each traffic lights, when all others seem to hate this technology, is for two reasons:
- unlike say BMW we mentioned in this thread, Mazdaās i-Stop is just a part of something bigger (the i-Eloop recuperation system) which I actually like the idea of (provided it works, of course
- when seeing the information on the fuel efficiency screen that i-Stop is ānot readyā and knowing itās due to the battery handling problems, I actually worry much more about the latter than inability to have the engine stopped and started automatically for me (this being said, in those my previous vehicles where their conventional Start/Stop system did work properly, I actually did like it sometimes - mostly during those long trip of mine, when a while of silence and nice music from the stereo systems did relax me a considerably)
Whatās also niice about it is the restarts are much smoother than in my other cars with conventional Start/Stop systems, where the starter has to be usedā¦
Mazdaās can have i-Stop without i-Eloop. The DCDC converter steps battery voltage up during restart on non i-Eloop cars, the DCDC converter steps capacitor voltage (24 volts) down during restart. On both systems the starter motor is supplied via the 12 volt lead acid battery for restart. On I-Eloop equipped cars the capacitor supplies power to convenience systems during i-Stop.
Also, Mazda I-Stop batteries are EFB (Enhanced Flooded Battery) and should be charged using a constant current not a constant voltage as most home chargers do.
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So, isnāt the Bosch C3 charger I use an optimum one?
No idea what a Bosch C3 charger is, sorry. Mazda supplied chargers for the dealer network are made by Fronius.
You see - and here is where my 50 years of experiences doesnāt help me at all, because:
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when I was young, and cars were built so simple that everyone could do amost anything maintaining them without a need of specialized equipment, a copper-made stripe was usually present connecting the engine metal parts to those of the body. So, it was easy to locate a spot which was the real ground (earth), with zero potential difference
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with todayās cars I have no idea if an where such an āabsolute zero potentialā location is present, with many plastic or aluminum joints/nuts etc
So even though I know itās not ideal to use the minus terminal of the battery, it doesnāt leave any doubts itās the āzero potentialā point. On the other hand, I know a guy who so badly desired not to use the batteryās negative post directly that he connected the zero cable of his charger toā¦ the aluminum tube between the heat exchanger to the compressor 
If you enlarge the picture of my battery I posted, you will see the writing on the white sticker in the upper left area āfor stop & startā.
I have spent an hour or so learning up on batteries this morning, but canāt find anywhere saying that using the AGM setting on a normal wet battery, or EFB will cause any harm, or vice versa. The differance (as above) is a slightly higher voltage (about 0.3v higher), so perhaps the settings optimise things, but I suspect the different modes have more to do with marketing than engineering. I have read that RECOND settings can damage AGM batteries, so would avoid that.
Iād also repeat (just for completeness) that if a battery is changed on āmodernā cars, then the computer needs to be told so it can recalibrate. Failure to do this can lead to premature failure of the new battery as it is incorrectly managed by the control systems.
Back to your battery specifically, as previously this looks like a wet battery to me, and doesnāt look maintenance free - which is surprising for one with a āstart stopā sticker on it. I would assume this was an EFB battery and would be using Mode 3, but I would not worry about it if I had used Mode 4. But I would still be suspicious about the provenance of this battery. It might well be 100% the correct type and manufacturer, but I would be doing some digging if it was me.
It is the correct battery, you can just see the code N-55 moulded into the battery top under the current sensor on the negative terminal. These are the codes that Mazda reference for all of their i-Stop batteries. T-110, Q-85, S-95 and N-55 from memory. They are all flooded batteries.
Hereās some reading for youā¦
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The reconditioning or whatever you like to call it setting is a setting where a shock current is pulsed through the battery to knock sulphation off the plates to expose fresh metal and get the battery functioning again.
Best avoided if not necessary I would have thought.
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Many thanks RR, that is comprehensive but raises a question. What ādamageā are we doing using smart chargers? I donāt think they get to the high voltage required and certainly donāt keep it at a constant.
Perhaps we just stick our head in the sand and keep doing what we do!
Could you elaborate further on what the current sensor is actually doing? TIA.
The answer to the OPās Title question is presumably no then.
Its a wet battery, not AGM, so donāt use the AGM setting.
As I said - due to i-Stop not working, Iām already with a 3rd battery unit from my Mazda Service (replaced under warranty), and they have all be the same.
Hi M,
To be honest I have no idea exactly what it does but it certainly does something as if it was not required it certainly would not be there. As I said it MAY upset things. It appears that voltage is very important to these batteries.
TIA is an interesting abbreviation, may be that is what is happening to the cars brain and again I do not know.
Are you using an āout of specā battery charger on yours? With the knowledge of RRs post this may explain why your car is eating batteries. But as lots of us are using them you would have thought there would be more battery failures on NDs showing on here.
I hope the problem with your car is sorted soon and please report the solution when it is found.
Thanks for the reading, Robbie - funny thing is that while the Bosh C3 was an excellent charger for all my BMWs and the Golf R, itās simply NOT a suitable charger for my i-Eloop/i-Stop equipped Miata (point 7 of Q&A in the pdf - none of the requirements is met :
).
PS. My only option seems to sell away the automatic C3 and buy myself something which does meet the criteria in point 7 of the Q&A. Which model would you guys recommend (available on-line in the EU))?
In a nutshell the current sensor monitors āchargeā (and IIRC, battery temperature) into and out of the battery and reports it to the PCM via a LIN communication. Itās used to calculate battery state of charge (SOC).
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