MG 4 & MG ZS EVs both dead - 12V flat while charging.

[brotherkennyh]

Hi all,

I have had a great couple of days owning MGs. Both cars went completely flat. Personally I think there is a design fault with the charging. Has anyone else had similar issues?

One car is an MG4 EV and the other is an MG ZS EV, both 2023 plate.

The only change on my part is that I have left them plugged in overnight and set charging to start as soon as the car is plugged in. Originally it was on a schedule. This is the only change.

The MG 4 EV was purchased approx. 3 weeks ago. So initially I contacted the dealer assuming there was a fault with the car. The car had no power at all. I had to unlock the car with the manual key. I even climbed into the car to unlock the EV charge socket from the manual release so I could charge the other car. The car was driven for an hour before being charged so the 12V battery should be been fully charged off the HV battery before connecting the EV charger.

The MG ZS EV is now also flat. We have had this car since last August plugged this in yesterday after managing to disconnect the charging cable from the other car. This car is now also completely flat. I had to unlock it with the manual key again. It brings up some warning about the 12V battery voltage on occasion, but otherwise the battery has not been a problem. Even when it brings up a warning message about the 12V battery being low the voltage shows at 13.8V.

I had the AA out to start the cars, both cars showed 3V in the 12V battery. They took a couple minutes to start-up and then took over charging the 12V battery from the HV battery.

The ZS was completely fine after charging. The MG4 has a whole list of systems that are not working, mostly drive assist systems. Its now booked in with a dealer for diagnostics.

I not I also contacted MG before booking into a dealer. They were really not helpful at all and the only suggestion they offered was that the EV charger must be at fault. They suggested I take the car to another charger and try that. Amusing considering at the time I had not called the AA so the cars would not move. To be clear the cars charge fine, its just that they discharge the 12V battery while charging. This is fine for a short duration charge, but if its left plugged in the car goes flat.

The EV charger does not charge the 12V battery so I can't see how the car can be blamed. The car is responsible for keeping its 12V battery charged and it seems to have been overlooked.

Cheers

Kenny

 

[Tight Git]

Have you checked that the 12V terminals are tight?

 

[brotherkennyh]

Hi,

Thanks for taking the time to respond. Yes, the terminals are fine. The car is also currently reading 12.4V. Its been off for a few hours now. It does go up to 14V when charging.

The 12V battery seems to be working ok, even if it has questionable behaviour when connected to a charging point.

Cheers

Kenny

 

[Martinonline]

As far as I know the HV battery is isolated when charging and the car is powered down and so it will not maintain the 12V battery. Your cars may have dodgy batteries or something draining the battery. Do you have dash cams?

EDIT: see @Kithmo post below, HV battery is not isolated during AC charging

 

[Kithmo]

As far as I know the HV battery is isolated when charging and the car is powered down and so it will not maintain the 12v battery. Your cars may have dodgy batteries or something draining the battery. Do you have dash cams?

From everything I've read, the 12V is also being charged when the HV battery is on an AC charge so not isolated.

I not I also contacted MG before booking into a dealer. They were really not helpful at all and the only suggestion they offered was that the EV charger must be at fault. They suggested I take the car to another charger and try that.

I tend to agree with MG on this, the only common thing about the two cars is the charger. Although the charger may be charging the HV battery ok it's obviously draining the 12V at the same time.

 

[CrustEE]

If the car is being charged by an AC charger (standard house to car charger), and the HV battery successfully charges, it cannot be held responsible for the charging of the 12V battery. The internal systems of the car manage that.

My neighbour's MG4 failed due to 12V battery a couple of months ago. The AA tested the 12V battery and stated that it had failed internally (at least one cell died). A new battery solved the issue.

 

[Lovemyev]

To try and therefore rule out any possibility of a drain by the wall box, what about using the MG supplied “Granny” lead to charge one of the cars and then monitor how this differs when charging from the wall box ?.
As you have two EV’s then have you not considered purchasing a 12 volt battery booster pack in case of a repeat of this type of incident ?.

 

[Coulomb]

The EVSE (external to the car) is not responsible for charging the auxiliary (12V) battery. The car's DC-DC does that, when in ready mode, or when charging, but not when waiting for a charge.

If the 12V battery is weak, it's possible that it could die before the charge begins. In that case, neither battery will get charged. The Mark 1 ZS EV needs something to wake it to start charging. Some EVSEs seem to be able to do that, I don't know how. So if you only recently switched to charging the ZS on a timer of some sort, that could explain the ZS 12V battery dying. The MG4 12V battery dying might be a coincidence, dying of a combination of old age and bad treatment waiting for shipment or the like.

 

[Martinonline]

@Kithmo, I am wrong and you are correct. Just experimented using my granny charger, battery went up to 14.3V when AC charging.

 

[Deleted member 9909]

12V charging should occur whilst charging, in aux/<ready mode/driving and when using v2l. Why? The control circuits for these functions all work off the 12V system and therefore need to be charged during operation. The HV battery does all the heavy lifting the 12V the intelligence...unfortunately in some cases

 

[Kithmo]

The MG4 12V battery dying might be a coincidence, dying of a combination of old age and bad treatment waiting for shipment or the like.

I agree it's possible, but one hell of a coincidence on both cars.
It may be that because they were plugged in for a long time the signal wire kept handshaking the car often and flattened the 12V.
ISTR, before an update, the first gen ZS wouldn't start to charge if you left it plugged in for more than a couple of hours before a schedule (on the charger) maybe this was to save the 12V going flat.

12v charging should occur whilst charging, in ready mode/driving and when using v2l. Why? The control circuits for these functions all work off the 12v system and therefore need to be charged during operation. The HV battery does all the heavy lifting the 12v the intelligence...unfortunately in some cases

FWIW, on the MG4 the 12V also charges in aux mode, i.e. as soon as you sit in the car and it boots up, before pressing the brake pedal to put it in ready mode. Check the voltage out on the TPMS page.

 

[Del 1731]

As an ex battery warranty manager and tester for platinum batteries any lead acid battery registering under 12.6V is considered as under charged/flat. anything over 13.2V is over charged there is a very fine line with batteries. personally I would swap out a normal lead acid battery for an AGM start stop. much more reliable battery. I've got gen 2 ZS also a vauxhall mokka 2015 with start stop agm battery and it's the original one. I would charge both 12V batteries and test them. they may have got a fault. We had to do a 5 point test before writing a battery off. not just use a tester. remember its not the voltage of a battery a battery can read 12.8V its the CCA if thats 20% less than what it should be then the battery has failed

 

[TassieDi]

It may be that because they were plugged in for a long time the signal wire kept handshaking the car often and flattened the 12V.

I agree with this suggestion. I have the same problem with my MGZS2022 - when charging has finished but the car is still plugged in to the 22kW EVSE, a regular handshake signal happens. With a 12V battery monitor attached you can see the voltage of the 12V battery slowly and steadily decline. I had one 12V battery ruined by this and several flattenings of the next one before other people in this forum helped me to work out what was going on. I recommend getting a 12V battery monitor and observing!

 

[brotherkennyh]

Hi all,

Thanks for the replies. I was surprised to see so many because I am no longer getting the email notification.

I have the car booked in at my local MG dealership for diagnostic and testing. However MG customer support suggested there is a software update. Unfortunately this isn't until 20th June.

The car has been fine since charging the 12V battery. I charged it again from the wall box last night. This morning is was showing 10.2V, but thankfully the car started and restored the battery charge.

I should say I am charging from a GivEnergy EV charger.

I have noticed the car registers approx 15V while charging from the wall.

I do agree with the comments that it's probably the charger handshake keeping the 12V circuits running after the HV battery has charged. It is charging the 12V battery as well at this point.

I am going to try with the granny charger.

My 7kW GivEnergy charger also has a plug and go feature. I think this might be keeping the handshake signal going and preventing the car from disabling the 12V circuit. I am going to try disabling it, so charging has to be started with a fob. This will disable the continuous handshake.

I will report back soon.

Cheers

Kenny

 

[tsedge]

As an ex battery warranty manager and tester for platinum batteries any lead acid battery registering under 12.6v is considered as under charged/flat. anything over 13.2v is over charged there is a very fine line with batteries. personally I would swap out a normal lead acid battery for an AGM start stop. much more reliable battery. ive got gen 2 zs also a vauxhall mokka 2015 with start stop agm battery and its the original one. I would charge both 12v batteries and test them. they may have got a fault. We had to do a 5 point test before writing a battery off. not just use a tester. remember its not the voltage of a battery a battery can read 12.8v its the CCA if thats 20% less than what it should be then the battery has failed

12.6V isn't flat. My MG4's 12V battery has worked flawlessly for 14 months now and varies between 12.2V (which is around 50% charged, not flat) and 14V (when being charged). This is similar to lots of other members. I appreciate you have expertise in this area but I am guessing it was with ICE, not EVs. We don't need to crank over an engine.

I'm late to the party but yes sounds like handshake drain / charger fault as both going flat on the same day is just too much of a coincidence - extremely unlikely.

 

[Phil H]

Hi all,

I have had a great couple of days owning MGs. Both cars went completely flat. Personally I think there is a design fault with the charging. Has anyone else had similar issues?

One car is an MG4 EV and the other is an MG ZS EV, both 2023 plate.

The only change on my part is that I have left them plugged in overnight and set charging to start as soon as the car is plugged in. Originally it was on a schedule. This is the only change.

The MG 4 EV was purchased approx. 3 weeks ago. So initially I contacted the dealer assuming there was a fault with the car. The car had no power at all. I had to unlock the car with the manual key. I even climbed into the car to unlock the EV charge socket from the manual release so I could charge the other car. The car was driven for an hour before being charged so the 12V battery should be been fully charged off the HV battery before connecting the EV charger.

The MG ZS EV is now also flat. We have had this car since last August plugged this in yesterday after managing to disconnect the charging cable from the other car. This car is now also completely flat. I had to unlock it with the manual key again. It brings up some warning about the 12V battery voltage on occasion, but otherwise the battery has not been a problem. Even when it brings up a warning message about the 12V battery being low the voltage shows at 13.8V.

I had the AA out to start the cars, both cars showed 3V in the 12V battery. They took a couple minutes to start-up and then took over charging the 12V battery from the HV battery.

The ZS was completely fine after charging. The MG4 has a whole list of systems that are not working, mostly drive assist systems. Its now booked in with a dealer for diagnostics.

I not I also contacted MG before booking into a dealer. They were really not helpful at all and the only suggestion they offered was that the EV charger must be at fault. They suggested I take the car to another charger and try that. Amusing considering at the time I had not called the AA so the cars would not move. To be clear the cars charge fine, its just that they discharge the 12V battery while charging. This is fine for a short duration charge, but if its left plugged in the car goes flat.

The EV charger does not charge the 12V battery so I can't see how the car can be blamed. The car is responsible for keeping its 12V battery charged and it seems to have been overlooked.

Cheers

Kenny

Had a similar problem with our ZS albeit it went flat when left undriven for 2 weeks. AA got it going but like yours, the 12V battery was at 3V. Took it in to the dealer and after a week, they told me the fix had been to reset the battery control module. I wasn’t convinced myself but it hasn’t gone flat since although it hasn’t been just parked up for any length of time since that happened.

 

[Coulomb]

remember its not the voltage of a battery a battery can read 12.8V its the CCA if thats 20% less than what it should be then the battery has failed

In an ICE car that has to start a cold engine with some 200A, yes. But in an EV, I suspect that 10A is enough to start it. So in an EV, the 12V battery could last longer than in an ICE.

 

[brotherkennyh]

I was honestly surprised they have a lead acid battery. I am sure there are better options available.

It should hardly use any power compared to cranking amps of an ICE vehicle. It has to power some electronics and a relay. Then the HV battery can take over. I think the various heating systems are 12V, but you don't need them on until the car is in ready mode.

Last night I tried the GivEnergy charger, but with plug and go disabled so it didn't maintain a handshake signal. This morning the car is fine. 13V. Gonna try the granny charger anyway just to see what happens.

I still think this is a design flaw on MGs part. Many smart chargers have a handshake signal like this. The car still needs to power its 12V battery.

I will mention this to MG to see what they say.

Cheers

Kenny

 

[decrep]

Just a simple supervisor cct, that stops the system when 12V battery gets too low would help.

 

[Coulomb]

I think the various heating systems are 12V, but you don't need them on until the car is in ready mode.

Heated seats and steering wheel are 12 V, but the main heater and air conditioner are high voltage. You need at least a kilowatt to merely move the needle on cabin temperature, and that's not convenient from 12 V.