Can I use this 12V battery on my MG4?

[tsedge]

But do you know if the battery currently fitted in the MG4 is WET or AGM? The recommended battery is listed as WET.

I don't know the answer to that.

 

[siteguru]

Does it matter?

 

[GameZone]

Does it matter?

Don't know. Some places say that AGM should be swapped for AGM.

 

[Ian Key]

Don't know. Some places say that AGM should be swapped for AGM.

Thanks to Google I found the following....

Can I charge an AGM battery with a regular charger?
AGM batteries don't have nearly as much internal resistance, which is how they absorb 30, 40, even 50 amps at a time instead of a regular battery getting stressed out at more than 10 amps. This is also why an AGM battery needs special charging. Regular battery charging can break AGM batteries.

Looks like you will have to stick to a normal "wet" lead acid battery.

 

[pecker]

Did anyone find a suitable leisure battery that fits ?

 

[GameZone]

Did anyone find a suitable leisure battery that fits ?

I found a regular battery from a quality manufacturer. No more errors or flat battery.

 

[pecker]

I found a regular battery from a quality manufacturer. No more errors or flat battery.

Which one did you order ?

 

[Yevgen K]

But do you know if the battery currently fitted in the MG4 is WET or AGM? The recommended battery is listed as WET.

WET

 

[Coulomb]

Thanks to Google I found the following....

Can I charge an AGM battery with a regular charger?
AGM batteries don't have nearly as much internal resistance, which is how they absorb 30, 40, even 50 amps at a time instead of a regular battery getting stressed out at more than 10 amps. This is also why an AGM battery needs special charging. Regular battery charging can break AGM batteries.

Looks like you will have to stick to a normal "wet" lead acid battery.

Sorry for the rather late reply. I'm about to replace my MG4's auxiliary battery, not because it seems to be directly causing any issues, but because the car has 5 annoying warnings on every start-up, including "Adaptive Cruise Control not available", and someone here said that their similar warnings went away with a new auxiliary battery. Research indicates that MG don't know how to fix this problem, and will likely refuse warranty repair, and quote some £1000 for replacing some entire ECU. I'm not convinced that this will even fix the issue.

So I want to eliminate the auxiliary battery potential issue first. So to the next question is: do I replace it with another ordinary lead acid battery, or an AGM, or Enhanced Flooded Battery (EFB), or something else.

I'm not convinced that AGM batteries require terribly special charging, as claimed in the quote above. The main problem is that they must not be over-charged, but it seems to me that the MG4 isn't going to push the battery voltage beyond 14.4 V. So that seems fine.

The AGMs seem to have lower internal resistance. It seems to me that this has three main effects:
1) It allows for higher loads, e.g. cranking. Not relevant to EVs.
2) It allows for higher charging current. It seems to me that this is an advantage, as the MGs seem to charge the auxiliary battery for too short a time (often only minutes) at ≥14.0 V. So with their lower internal resistance, AGMs can absorb more charge during that short time with the high charge voltage. The DC-DC is capable of some 178 A, so even with power steering and other high current loads, it doesn't seem that DC-DC current rating will be an issue. As a bonus, the surge of high charge current may stir the electrolyte, reducing premature degradation due to stratification. Though with the acid trapped into fibreglass mats in an AGM battery, perhaps this is not relevant.
3) It keeps the "14 volt bus" more steady for sensitive electronics. This is the only reason I can see that replacing the auxiliary battery would affect ECU operation. It's a widely held view that problems with the auxiliary battery can affect all manner of car systems, often causing a variety of trouble codes to be logged. So when a large number of fault codes comes up and they seem to be unrelated, the received wisdom seems to be that the auxiliary battery is on the way out. I've seen it stated here that once the car is started, you could actually disconnect the auxiliary battery and the car would continue to run unaffected. My view is that actually such disconnection would greatly destabilise the "14 volt bus", causing all manner of problems.

So effects 2) and 3) above seem to favour AGM batteries, and indeed any battery that has low internal resistance. The easy way to select for low internal resistance may be to opt for batteries that claim to be optimised for start/stop operation, despite the fact that EVs don't have that behaviour.

In my research, I've not been impressed with the EFB (Enhanced Flooded Battery), but that's more of a gut feeling than solid reasoning. So I've decided to replace it with an AGM battery.

I think it would be great to come up with a consensus about what type of battery we should be replacing our failed auxiliary batteries with, once and for all.

Anyone that has replaced their auxiliary battery, please comment on which type you chose, perhaps with a short summary of why you made that choice, and what the results were. I suppose that any new battery is likely to perform adequately for several years; only the long term will really tell. But we must have some members that have replaced their auxiliary battery 4-6 years ago, and the factory auxiliary battery doesn't seem that great. So some valuable data must be out there.

 

[Coulomb]

Did anyone find a suitable leisure battery that fits ?

I don't believe that it's practical to replace an EV auxiliary battery with a leisure / deep cycle battery. Deep cycle batteries tend to come with threaded studs rather than automotive posts. The whole idea of deep cycle batteries is to supply low currents for many hours. They are not supposed to be charged or discharged at particularly high rates, i.e. at high currents. This is not really the case with EVs. An EV auxiliary battery may be called on to take over powering the "14 volt bus" in the unlikely but certainly possible situation where the car's DC-DC converter has failed. It is then running all the computers, power steering (a very heavy load), all lights, brake assistance pump, wipers, HVAC fans, and so on.

The DC-DC may decide to charge the auxiliary battery fairly quickly, and indeed it needs to do that for the common case of many 10 minute trips to the local shops. A 12 hour slow charge, as preferred by a deep cycle battery, is just not practical.

So I think that this persistent idea that EVs should really be supplied with deep cycle batteries is not correct. But I'm happy to hear arguments for and against.

 

[Jef]

Does the car require any programming to accept a replacement battery or is it fit and forget?

 

[siteguru]

Programming?

It's a 12V battery .. the only things needing to be done are the usual things if you'd simply disconnected the original battery - reset window controls, recentre the steering wheel, etc.

 

[mg4mc]

Lots of ice cars have a programming option for a battery replacement - I think it resets the car's memory of how much charge/voltage to give etc. as they adapt as the battery ages. My Golf had this, you could also change the battery type LA, AGM, etc.

 

[Jef]

Thanks all

 

[Coulomb]

I'm about to replace my MG4's auxiliary battery, not because it seems to be directly causing any issues, but because the car has 5 annoying warnings on every start-up, including "Adaptive Cruise Control not available", and someone here said that their similar warnings went away with a new auxiliary battery.

I finally did the replacement this afternoon. Alas, it did not fix my issues, but it's good to have eliminated the auxiliary battery as a potential cause.

Something that gave me hope that the auxiliary battery might be the issue is that after three cycles of unlock, open door, close door, and wait 2 minutes, the auxiliary battery voltage dropped as low as 12.1x volts. Now with the new battery under these conditions, it drops only to 12.4x volts. The resting voltage a few hours after switch off has increased from around 12.6x volts to 12.9x volts, but that's probably mostly because the new battery is of the Absorbed Glass Mat type (AGM).

I measured the drain soon after opening and closing the door at over 10 amps, dropping to various plateaus over about 5 minutes to under 50 mA, including some 1.5 mA for the battery monitor. At that point I got tired of holding the multimeter leads. With both batteries, the voltage drops a fair bit when the door is opened, and recovers several tenths of a volt as the load decreases.

 

[Coulomb]

I finally did the replacement this afternoon. Alas, it did not fix my issues...

Today the five systems (ACC, speed sign detection, etc) came good by themselves! Eighteen days later!

Now I think it really was the auxiliary battery after all, and it needed a long drive to clear it, or a certain distance driven. At present, I have mostly been doing very short trips, to and from shops, doctors, etc. Maybe it took a long time to "learn" that the ordinary lead acid battery is now an Absorbed Glass Mat (AGM) type.

Of course, it might just be intermittent, so time will tell. But I'll take the win for now!

Edit: Maybe if I had the software to "program" the battery change, it might have come good immediately?