iStop Two Battery Charging System?

[Bulld0g]

Hi guys,

I have a 2012 Mazda 5 with istop so has two batteries.

Do these Mazda's have a smart alternator and if not how does the charging system work with the two batteries?

The reason I need to know is that I use a leisure battery in my boot that I need to take out to charge so would be really handy if I could change it from the car.

I was thinking about using a split charge relay and maybe connecting it to the smaller battery but I read somewhere that the split charge relay may not even be necessary at the car already has the capability to change multiple batteries.

 

[negusm]

Not familiar with this istop system but have questions...

Are all batteries 12v?

If so, why wouldn't they all just be wired in parallel to the alternator?

You might need a beefier alternator for the current requirement, but you shouldn't need anything "smart" at all. You just need to know what the alternator max current output is and whether it can charge all 3 batteries. To the alternator, three 12v batteries in parallel just looks like a single larger 12v battery.

I'd like to know if I'm missing something but it seems like simple electricity\circuit rules apply.

 

[Bulld0g]

Not familiar with this istop system but have questions...

Are all batteries 12v?

If so, why wouldn't they all just be wired in parallel to the alternator?

You might need a beefier alternator for the current requirement, but you shouldn't need anything "smart" at all. You just need to know what the alternator max current output is and whether it can charge all 3 batteries. To the alternator, three 12v batteries in parallel just looks like a single larger 12v battery.

I'd like to know if I'm missing something but it seems like simple electricity\circuit rules apply.

Thanks for the reply.

This is a good thread about the batteries:

B

Guide Thread 'Mazda5 with iStop - How to select and install both batteries'

Dec 23, 2015

The oldest of the second gen Mazda5's with istop are getting to about 4/5 years old now, and for most owners the batteries will be fairly tired, and your car will be out of warranty.

For those that don't know, the 2.0 DISI Mazda5 has the iStop system which is a forerunner to the full Skyactive e-Loop system. Basically the car has a main, larger, start/stop battery and a smaller battery bolted next to it that runs the ancillaries when the car is in auto shut-off mode. Both batteries were designed and built for Mazda by Panasonic.

The problem is, a dealer will charge you 250+installation...

• Bodgerx
• Replies: 10
• Forum: Mazda5 Forum

• 

I would expect the batteries to be changed in parallel but I wanted to make sure that Mazda didn't come up with some strange system.

The alternator is meant to be a heavy duty one but I also wanted to make sure it's not a smart alternator.

 

[Bulld0g]

It seems that the larger battery charges independently from the smaller battery.

It's really strange there isn't more information about the charging circuit on this system.

 

[negusm]

What does that mean, "independently"?

Just go and put a multimeter on the battery and alternator and check for continuity. The alt probably has a direct connection to the positive posts of both batteries. There probably isn't any information because it's just a normal charging circuit.

Regardless, you can consult the Factory Service Manual (FSM). That will have the circuit diagram on it. You can't work on modern cars without it.