"12 volt battery charge low avoid parking for more than 3 days" message

[pollenface]

12.1v indicates heavy sulfation, capacity loss, replace ASAP.

 

[TreeBadger]

I am leasing a new MG5 since December. We started getting these messages every day after 6 months. The 12V battery was replaced under warranty about a month ago. Now the same warning messages are coming back on a new battery. We use the car normally, don’t let it sit for long periods. I think it’s just a very very poor design. Something is draining the 12V but we’ve no idea what it is. I suppose we just need to keep a jump start with us and ignore it I guess.

Hi, as others have said, try disconnecting the 12V battery, leave it for a few minutes and then reconnect it. It'll throw up a bunch of error messages, but they'll soon clear once you drive the car. It worked fine for me and I've had no further issues with it. You'll only have to disconnect and reconnect the 12V battery once and it should solve the problem. I hope this helps.

 

[Area808]

Hi, as others have said, try disconnecting the 12V battery, leave it for a few minutes and then reconnect it. It'll throw up a bunch of error messages, but they'll soon clear once you drive the car. It worked fine for me and I've had no further issues with it. You'll only have to disconnect and reconnect the 12V battery once and it should solve the problem. I hope this helps.

Hi there, I did try this and miraculously after a flurry of every warning message under the sun it did indeed start displaying a full 12V charge and the 12V warnings disappeared.

So it's some kind of software/communication issue then I suppose.

Thank you, will monitor for now but hopefully that is indeed the end of it, because it is the most tedious issue ever.

 

[TreeBadger]

Hi there, I did try this and miraculously after a flurry of every warning message under the sun it did indeed start displaying a full 12V charge and the 12V warnings disappeared.

So it's some kind of software/communication issue then I suppose.

Thank you, will monitor for now but hopefully that is indeed the end of it, because it is the most tedious issue ever.

You're most welcome. I'm pleased that's resolved it. As you say, best to monitor it. If you don't receive the error message, but still find the level has dropped somewhat when you check it on the display in the car, I believe pre-cooling the car from the app will get the 12V battery back up to 100%.

 

[Area808]

You're most welcome. I'm pleased that's resolved it. As you say, best to monitor it. If you don't receive the error message, but still find the level has dropped somewhat when you check it on the display in the car, I believe pre-cooling the car from the app will get the 12V battery back up to 100%.

Another top tip! Cheers.

 

[Staffex]

The section below, pasted from MG5 Supercharger: FAQ 2 - What upgrades does my MG5 need to use a Tesla charger? 2 advises getting update SC052 done. For 2 years running I've asked my dealer, Wilsons Epsom, to install it but on each occasion I'm told that no such update exists. The technician said that he'd gladly co-operate if I could provide more information. Is SC052 still available and can anyone give precise details that would enable my dealer to locate and install it?

What software upgrades are necessary?

There are two: SC052 and the EVCC fix. The SC052 EP22£EP21£ZS11EMCE CCU Software Update will not fix the Tesla problem on its own but it does address the HV battery fault alert caused by the 12V battery not providing a high enough voltage to start the system. This is done by raising the DCDC battery voltage to around 14.6V thus allowing the 12V battery to be fully charged. It does improve the CCS charging reliability - presumably because the 12V voltage is a bit higher - so it is worth making sure it is done. It is a warranty FOC repair. The EVCC fix can be carried out at the same time - mine was - but that is according to MG, chargeable.

Even if you do not have the EVCC fix, make sure that the SC052 update has been done.

 

[pollenface]

I notice 14.7v while charging, 14.2 while driving.

 

[Staffex]

I notice 14.7v while charging, 14.2 while driving.

When the car isn't driven, its 12v lead-acid battery gradually discharges until the voltage drops below a predetermined threshold, the DC-DC converter then turns on, recharging the 12v battery from the traction battery. Problems occurred because this threshold voltage was originally set too low, leaving insufficient charge on the battery to reliably run the car. It's my understanding that the SC052 software update addresses this problem by raising the threshold voltage, thus maintaining the 12v battery at a higher state of charge.

The received wisdom is that a fully charged 12v lead-acid battery should register 12.6v; it should be recharged if it drops below 12.45v. Mine falls below this when the car has been parked for several days so I've taken to using the MG app to remotely turn on the aircon, which also brings on the DC-DC convertor to start charging the 12v battery.

Despite what has been written about update SC052, my dealer cannot locate it and he questions the reliability of information given on this forum. I'd greatly appreciate it if someone could post sufficient information here to prove him wrong.

 

[MickeySw]

When the car isn't driven, its 12v lead-acid battery gradually discharges until the voltage drops below a predetermined threshold, the DC-DC converter then turns on, recharging the 12v battery from the traction battery.

This functionality has indeed been mentioned in MG5 marketing materials, but it was never implemented. In reality the 12V aux is only charged when the car is READY, charging or in Pre- Heat/Cool mode.

 

[Staffex]

This functionality has indeed been mentioned in MG5 marketing materials, but it was never implemented. In reality the 12V aux is only charged when the car is READY, charging or in Pre- Heat/Cool mode.

Thanks Mickey, on checking I've found you're right.

When I received my car in 2023 I printed out the entire owners manual; yes I know it sounds bonkers but I wanted a hard copy. On page 9 there's a section below Equalisation Charging headed Intelligent Charging which states: "The 12V battery SOC is constantly monitored, when the Start/Stop switch is in the OFF position it is possible, under certain conditions, that the HV battery will automatically charge the 12V battery to ensure the vehicle starts. This function will activate and switch off automatically.".

FYI I was going to cut and paste that quote from the latest MG5 manual https://www.mg.co.uk/sites/default/files/2021-11/MG5 EV Owner Manual.pdf
but I found a blank space where the Intelligent Charging paragraph once existed. I wonder why MG chose to either remove - or not implement - what seems to be a very sensible feature?