Information on the 12V Battery.

Tried to see if anything has been posted on this before but couldn't find anything.

Can anyone advise me what voltage a healthy 12V battery in the MG4 should be reading?

I've always understood that a fully charged healthy car battery should show about 14.1V and a battery giving just over 12v could be considered to be at the lower end of charge.

I picked up my MG4 a couple of days ago and I noticed that the 12V battery was showing over 14V for the first day but has dropped steadily to just over 12V. I've not been doing anything to discharge it but have seen several mentions of faulty or poor-quality batteries fitted to some MG4s.

I've had no problems with the car and it has run well since I got it but thought I would be proactive and ask if anyone has any thoughts on what I could expect the normal voltage range to be.

Any thoughts welcome.

In a typical lead acid battery, above 14v would be part of the charge cycle and can go between 14.4v to 15v in the bulk part of a charge cycle. Depending on the type (agm, leisure ect) (I imaging this is a leisure type as an EV doesn't need the cranking amps of a ice car) above 12.6 to 12.9 v would be fully charged. 12.4v or below would be partially discharged. 12.1v would be considered fully discharged

Purclewan said:

Tried to see if anything has been posted on this before but couldn't find anything.

Can anyone advise me what voltage a healthy 12V battery in the MG4 should be reading?

I've always understood that a fully charged healthy car battery should show about 14.1V and a battery giving just over 12v could be considered to be at the lower end of charge.

I picked up my MG4 a couple of days ago and I noticed that the 12V battery was showing over 14V for the first day but has dropped steadily to just over 12V. I've not been doing anything to discharge it but have seen several mentions of faulty or poor-quality batteries fitted to some MG4s.

I've had no problems with the car and it has run well since I got it but thought I would be proactive and ask if anyone has any thoughts on what I could expect the normal voltage range to be.

Any thoughts welcome.

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My MG4 shows a different voltage depending on whether it is charging the 12V battery or not. On the health check I have typically seen 12.3-12.7V when it is not being charged and about 1 volt more when it is being charged. Others have seen 14V on occasion. I have not had any problems so far due to battery voltage.

memo said:

In a typical lead acid battery, above 14v would be part of the charge cycle and can go between 14.4v to 15v in the bulk part of a charge cycle. Depending on the type (agm, leisure ect) (I imaging this is a leisure type as an EV doesn't need the cranking amps of a ice car) above 2.6 to 12.9 v would be fully charged. 12.4v or below would be partially discharged. 12.1v would be considered fully discharged

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I don't think the SAIC battery is a leisure battery, I think it is a low-end ICE small car battery.

I've got one of these, if I can find it, which I'm going to plug in and see when the 12v battery is charging just to get an idea of what's happening.

Chart here https://axleaddict.com/auto-repair/car-battery-voltage

Ian Key said:

I've got one of these, if I can find it, which I'm going to plug in and see when the 12v battery is charging just to get an idea of what's happening.

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memo said:

In a typical lead acid battery, above 14v would be part of the charge cycle and can go between 14.4v to 15v in the bulk part of a charge cycle. Depending on the type (agm, leisure ect) (I imaging this is a leisure type as an EV doesn't need the cranking amps of a ice car) above 2.6 to 12.9 v would be fully charged. 12.4v or below would be partially discharged. 12.1v would be considered fully discharged

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Thanks for the replies. I will continue to monitor the 12v battery but it seems that from the collective experience 12.5V should be a fair average.

I'm curious to know how the 12V battery is charged (and what would discharge it). Lots to learn about my new toy.

I suppose it is easy to get a bit paranoid about battery voltage when you hear of cars being dead for no apperently reason when their owners try to use them first thing in the morning.

Purclewan said:

Thanks for the replies. I will continue to monitor the 12v battery but it seems that from the collective experience 12.5V should be a fair average.

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Yes.

Purclewan said:

I'm curious to know how the 12V battery is charged (and what would discharge it). Lots to learn about my new toy.

Click to expand...

It is charged by the HV battery and should be topped up automatically when needed.

It runs everything in the car except the drivetrain and inverter/charger. Like in an ICE all your instruments, entertainment, lights etc... run off the 12V battery.

If you sit in the car with the HV battery off (via the safety menu you can power it down) you will discharge the 12V battery and if done for a long period it could go flat - just like an ICE car without the engine and alternator running.

Dead battery cars have typically been caused either by a faulty 12V battery (the MG one is the cheapest of the cheap), bugs in the system leading to the HV battery not keeping it charged, loose battery terminal cables (maybe disconnected for the sea voyage?).

Read here for some info. The 12v system is required whilst HV charging to control the Battery Management System, charge signalling etal hence the reason it will be topped up during charging or whilst using VTL (vehicle to load) to keep it "healthy".
As tsedge states it can discharge if you are sitting in the car in a not ready state with radio, lights etc. all active

Im an electronics engineer who has been involved in battery monitoring and charging.

The typical CHARGING voltage of a lead acid battery is 13.8 to 14.4 volts but can go as high as 14.8 in some vehicles.

The resting NOT CHARGING no load voltage of a new in peak condition battery is 12.8 volts.

the app is telling me mine is at 12.5-12.6v parked - bear in mind its accurate to probably 1% or so.

The discharged voltage will depend on the battery itself, and if it’s designed for deep discharge. 11.5v ish would be approaching critical for a standard car battery and 10.5v is appropriate for a deep discharge battery.

Bear in mind an unloaded and loaded battery voltage can be totally different and can collapse under a small load if “flat” even if it reads say 11.5v.

Once a battery goes below its lowest recommended voltage it will never come back to its original capacity

For the nervous types, looking at my car there seems to be space for a much longer battery if that takes your fancy.

Its got a small 45 amp battery which is about as small as they come. Which doesn’t necessarily imply a problem as my 1991 mx5 has the same battery.

Is also seems a bit of disassembly is needed as the strut brace runs over the top of the battery.

stevegus said:

For the nervous types, looking at my car there seems to be space for a much longer battery if that takes your fancy.

Its got a small 45 amp battery which is about as small as they come. Which doesn’t necessarily imply a problem as my 1991 mx5 has the same battery.

Is also seems a bit of disassembly is needed as the strut brace runs over the top of the battery.

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Stevegus, since you have expertise in this area - can you confirm if a leisure battery would be a good choice as a replacement?

FWIW my app is showing 12.2V right now. When I scanned yesterday it showed 12.1V. (I've not driven the car since last Wed evening, but will be going out this afternoon). When it is charging (e.g. when I'm driving or when the car is on charge) then I typically see 14.4V or thereabouts.

Purclewan said:

Tried to see if anything has been posted on this before but couldn't find anything.

Can anyone advise me what voltage a healthy 12V battery in the MG4 should be reading?

I've always understood that a fully charged healthy car battery should show about 14.1V and a battery giving just over 12v could be considered to be at the lower end of charge.

I picked up my MG4 a couple of days ago and I noticed that the 12V battery was showing over 14V for the first day but has dropped steadily to just over 12V. I've not been doing anything to discharge it but have seen several mentions of faulty or poor-quality batteries fitted to some MG4s.

I've had no problems with the car and it has run well since I got it but thought I would be proactive and ask if anyone has any thoughts on what I could expect the normal voltage range to be.

Any thoughts welcome.

Click to expand...

The MG iSmart app scans the car each time you click on it and tells you the 12v charge level.

tsedge said:

Yes.

It is charged by the HV battery and should be topped up automatically when needed.

It runs everything in the car except the drivetrain and inverter/charger. Like in an ICE all your instruments, entertainment, lights etc... run off the 12V battery.

If you sit in the car with the HV battery off (via the safety menu you can power it down) you will discharge the 12V battery and if done for a long period it could go flat - just like an ICE car without the engine and alternator running.

Dead battery cars have typically been caused either by a faulty 12V battery (the MG one is the cheapest of the cheap), bugs in the system leading to the HV battery not keeping it charged, loose battery terminal cables (maybe disconnected for the sea voyage?).

Click to expand...

Thanks for that info, very helpful. It was as I suspected but I was concerned about running the battery down if I was just sitting in the car listening to music whilst waiting for the wife to finish her shopping.

Buster72 said:

The MG iSmart app scans the car each time you click on it and tells you the 12v charge level.

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Yup, found that thanks. Steep learning curve.

siteguru said:

FWIW my app is showing 12.2V right now. When I scanned yesterday it showed 12.1V. (I've not driven the car since last Wed evening, but will be going out this afternoon). When it is charging (e.g. when I'm driving or when the car is on charge) then I typically see 14.4V or thereabouts.

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This matches my experience which was why I asked the initial question. As @stevegus mentioned batteries approaching 12V are heading into discharged territory. Mine seems to have settled around 12.4/12.6 so I guess there is nothing to be concerned about. Anyway, I really appreciate all the suggestions and help. Gives me some reassurance.

Purclewan said:

Thanks for that info, very helpful. It was as I suspected but I was concerned about running the battery down if I was just sitting in the car listening to music whilst waiting for the wife to finish her shopping.

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Put the car in park, and READY mode, then the 12 volt will stay charged from the traction battery with out problems also if it dark switch of the lights on the lighting switch to save a bit more in this state it would probably be ok for days if you wanted to do that.
But ready mode is the key the biggest drain really is the HVAC system but even using that shouldn’t give you an issue for a very long time.
Les

Les burrows said:

Put the car in park, and READY mode, then the 12 volt will stay charged from the traction battery with out problems also if it dark switch of the lights on the lighting switch to save a bit more in this state it would probably be ok for days if you wanted to do that.
But ready mode is the key the biggest drain really is the HVAC system but even using that shouldn’t give you an issue for a very long time.
Les

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Thanks Les, ready mode it is then. Much appreciated.

I'm just back from having been out in my car ... scanning with the app just now shows me 12.8V.

Yeh that fits. Took mine out for a run a couple of hours ago and it measured 14.4V when I got back. Measured it again 5 min ago and it is back down at 12.8V. Seems to fit with what @stevegus said. The full charge shows over 14V but then the battery settles to a quiescent state of around 12.6V.

I think I can stop being paranoid about battery quality.

To ease any flat battery concerns you have going forward, you could always keep something like this handy in the car Interior for emergency starts. You hopefully never need it but just in case...

NOCO Boost Sport GB20 500A 12V Portable Lithium Jump Starter

In theory it should be much less of a problem on an EV, as you dont need the cranking current to start the car - but the only issues I've had with my previous car (which I've kept as a backup), is to do with the 12v battery - 4 years ago, my earth strap failed - AA sorted it using a "temporary fix", which I had in my shed, of fitting a "new" earth lead - still working now!, and 2 years I had a new battery "fail" - but the company Tayna / Varta - simply serviced it (i.e. charged & cleaned the terminals) - and no problems since

Purclewan said:

Yeh that fits. Took mine out for a run a couple of hours ago and it measured 14.4V when I got back. Measured it again 5 min ago and it is back down at 12.8V. Seems to fit with what @stevegus said. The full charge shows over 14V but then the battery settles to a quiescent state of around 12.6V.

I think I can stop being paranoid about battery quality.

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Might be worth checking the 12v battery terminals are tight. There are a few cases where one has been loose which won't help in keeping it charged.