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[Kevin Wood]

Currently boiling away...

That's never good for an AGM. 

[TheBoy]

AGMs do need an AGM compatible charger.  Due to both a slight voltage difference, and due to it needing a more constant current, which older, cheaper cr battery chargers dont give.

It could be a switch/setting called AGM, or Stop/Start (as such stupidly equipped cars always use AGM)

[Marks DTM Calib]

I'd use a smart battery charger, not a traditional type, and set it to the reconditioning / repair setting which goes through a staged reconditioning cycle, rather than just blasting charge into it regardless. Depending on the reason for the low voltage, or how long it has been left in that condition, you may (possibly) recover it, but standing with a low state of charge doesn't do a battery any good.
But you must know this..
Depending obviously on where you sourced the car from, is there no redress from them?

They don't work, must have tried it 30+ times in the last 7 years with a Ctek and homebrew device on many different batteries and it never made a jot of difference. Which is actually not that surprising, as all its doing is pulsing some higher frequency charge to try to soften any sulphate build up. Have found a decent charge and maybe a balance charge works the best but, if its a tired battery then little can be done 

[Marks DTM Calib]

AGMs do need an AGM compatible charger.  Due to both a slight voltage difference, and due to it needing a more constant current, which older, cheaper cr battery chargers dont give.

It could be a switch/setting called AGM, or Stop/Start (as such stupidly equipped cars always use AGM)

If the charger is sub say 7A peek, then there is little difference, its only when its a high current charger that it needs to switch mode based on a different voltage level, basic chargers it makes no difference 

[TheBoy]

AGMs do need an AGM compatible charger.  Due to both a slight voltage difference, and due to it needing a more constant current, which older, cheaper cr battery chargers dont give.

It could be a switch/setting called AGM, or Stop/Start (as such stupidly equipped cars always use AGM)

If the charger is sub say 7A peek, then there is little difference, its only when its a high current charger that it needs to switch mode based on a different voltage level, basic chargers it makes no difference 

Good to know, although I thought AGM batts could be damaged by old chargers - the transformer > rectifier > battery type?

[Sir Tigger KC]

AGMs do need an AGM compatible charger.  Due to both a slight voltage difference, and due to it needing a more constant current, which older, cheaper cr battery chargers dont give.

It could be a switch/setting called AGM, or Stop/Start (as such stupidly equipped cars always use AGM)

Do cars with AGM batteries have different alternators?   

[Marks DTM Calib]

AGMs do need an AGM compatible charger.  Due to both a slight voltage difference, and due to it needing a more constant current, which older, cheaper cr battery chargers dont give.

It could be a switch/setting called AGM, or Stop/Start (as such stupidly equipped cars always use AGM)

If the charger is sub say 7A peek, then there is little difference, its only when its a high current charger that it needs to switch mode based on a different voltage level, basic chargers it makes no difference 

Good to know, although I thought AGM batts could be damaged by old chargers - the transformer > rectifier > battery type?

No more damage than they do to a sealed standard lead acid......

[Marks DTM Calib]

AGMs do need an AGM compatible charger.  Due to both a slight voltage difference, and due to it needing a more constant current, which older, cheaper cr battery chargers dont give.

It could be a switch/setting called AGM, or Stop/Start (as such stupidly equipped cars always use AGM)

Do cars with AGM batteries have different alternators?   

No, well there is not a specific alternator designed for them

Modern alternators (so those in the last 10-20 years) have a data connection (usually LIN) to the PCM (Powertrain Control Module). This allows the PCM to vary the output dependent on engine load, so for example, lots of load on a cold start diesel to get it warm faster, lots of output under braking as its free energy etc etc. This helps economoy but, also allows the PCM to modify the output of a 'standard' alterntor dependent on battery chemistry

[Doctor Gollum]

For better or worse, this is what I went with...

https://www.ringautomotive.com/en/product/RSC808

According to the destructions it is AGM suitable, unlike my Helfrods one which says in about 6 different places that it must not be used on AGM batteries...

From what I saw watching it yesterday, it seems to vary the voltage being fed to the battery.

[Sir Tigger KC]

Didn't you get a warranty from the dealer? 

[Marks DTM Calib]

For better or worse, this is what I went with...

https://www.ringautomotive.com/en/product/RSC808

According to the destructions it is AGM suitable, unlike my Helfrods one which says in about 6 different places that it must not be used on AGM batteries...

From what I saw watching it yesterday, it seems to vary the voltage being fed to the battery.

They all work the same, they start in constant current mode (so vary the voltage to maintain the constant current) to deliver the bulk charge (upto about 80% charged), then when it hits the peak battery voltage it maintains a constant voltage and the current starts to drop, this is the absorption charge. Then it goes into a float mode to keep it topped up.

Smart chargers claim more modes but, they are just sub levels of these three and they might do a better job on the float charge by turning the charger off for periods whilst monitoring the battery terminal voltage.

The major difference between AGM and standard is the peak battery voltage which is circa 100mV different, no major issue on a charger which is only putting a bit of power out.

[Doctor Gollum]

Didn't you get a warranty from the dealer? 

Probably, but I fully expected to put a battery in it and it would be akin to asking them to top up the screen wash or replacing a failed bulb

Obviously if the issue proves to be something more substantial then I will be having that conversation with them

[johnnydog]

AGMs do need an AGM compatible charger.  Due to both a slight voltage difference, and due to it needing a more constant current, which older, cheaper cr battery chargers dont give.

It could be a switch/setting called AGM, or Stop/Start (as such stupidly equipped cars always use AGM)

Not entirely correct. Not all cars equipped with Stop /Start systems have AGM batteries. Many use EFB batteries which is a cheaper alternative. However AGM batteries require charging on the AGM setting, but EFB batteries  can use the standard charging setting on a smart charger.

[Doctor Gollum]

Showing 7.1v when I put it back on charge.

[henryd]

Showing 7.1v when I put it back on charge.

I would say that's Donald