12v dead battery and wife locked in the car! - Welcome home!!

[drugrunner]

After a 7day holiday, return to Gatwick Long Stay South car park to pick up our MG4. Eventually find car which isn't responding to the fob to show me where she is.
Doors - don't open!
Call to the AA - 2hrs atleast!
I can't open the drivers door with the emergency key so go and guard our luggage by Bus stopD12 whilst wife has a go!
Get a phone call from the wife- she's manged to use the manual key and open the drivers side door, got in, door closed behind her and now she's locked in the dead car with both key fobs!
Panic call to AA, they set us as a priority!

Drag bags to the car. Wife crawls inside the car to the boot and manages to unlock boot manually using the emergency key from inside! Using the latch outside, I manage to open the boot and get her out!

Immediate panic over!

Still have a 3hr drive home to Dorset!

AA man arrives after 2hrs, boosts the 12v battery and the car comes to life!

First time we've take the car far away from home and parked for 7days!
HV battery was parked with 37% life! Have retrospectively checked 12v battery leads all look ok.
Had a software update to fix Bluetooth issues 1 week ago!
Could the new R33 update be causing battery drain?
Separately, I've read other posts about 12v batteries that die after 2 days or even 2hrs.
To be honest although I enjoy driving the MG4 I'm now a disappointed and concerned owner. Car bought new in April 23.
Will be calling Hendy Poole on Monday!

 

[fnegroni]

As per user manual, the car should not be stored for a long time with the HV battery at less than 50%

The intelligent battery maintenance system might decide that it’s better to not drain the HV battery and therefore might decide not to keep the 12v battery charged.

Whether the 12v battery should last a week without being charged, that very much depends on its health: even brand new batteries should be trickle charged to full before being installed. I tricked charged mine and it took a few hours more than the intelligent battery management would have charged it for to get to 100%. And 12v AGM batteries should be kept as near 100% as possible.

My advice is that you either trickle charge your battery to 100% yourself now and hope you can rescue it (ie: it will work as intended from now on) but my advice would be get a brand new battery, trickle charge it to100% (a NOCO trickle charger is cheap and will do a great job) note: even a brand new battery might need several hours before it is 100% charged.
This will ensure the new battery will not die within one week.

 

[siteguru]

This thread disappeared when I tried to reply earlier ... here's what I originally replied:

This has happened to a few people. The common theme seems to be that the HV battery was<50% SoC so it didn't keep the 12V battery topped up.

I was away on holiday for a week (came back on Thursday) and left my car at offsite parking. When I came back everything started up just fine. However my SoC was around 75%.

 

[Rolfe]

I was away for over a fortnight and the car was fine. (Just as well because it was three in the morning and threatening rain when we got back.) The HV battery was at 69% when I parked it, and it was still there when I got back.

I remembered reading something, maybe in the handbook, about leaving the car with a high SoC if parked up for a while. The car park had EV chargers available and if I'd been concerned I'd have used one before parking up, but I thought 69% would be OK.

I had also read something on the forum about the 12v not being topped up if the HV is below 50%, which seems bloody ridiculous to me, but maybe it's fair warning. On the other hand someone in another thread who had had no trouble when he left his car for several weeks, reported a dead car some time later after only a day and a half inactivity and again at a high HV SoC. Sounds like a different fault though.

 

[lfc958]

Took wife's LR to Gatwick , 100% leaving home with around 65% on arrival at airport parking. Away for 7 days came back to same %, no issues. No further updates since collecting car back in March.
I pick up my ER this week so am tempted to get a mini NOCO jump pack as we use the big ones in work they get well used and have been very reliable so can recommend based on experience.

 

[Rolfe]

The thing that worries me about these is that I hear they tend to die permanently if not kept charged up every couple of months. I'm likely to forget all about it. I need something that won't be ruined if I leave it untouched for a long time.

 

[AB71]

My partner said after reading the title is that such a bad thing

 

[drugrunner]

I was away for over a fortnight and the car was fine. (Just as well because it was three in the morning and threatening rain when we got back.) The HV battery was at 69% when I parked it, and it was still there when I got back.

I remembered reading something, maybe in the handbook, about leaving the car with a high SoC if parked up for a while. The car park had EV chargers available and if I'd been concerned I'd have used one before parking up, but I thought 69% would be OK.

I had also read something on the forum about the 12v not being topped up if the HV is below 50%, which seems bloody ridiculous to me, but maybe it's fair warning. On the other hand someone in another thread who had had no trouble when he left his car for several weeks, reported a dead car some time later after only a day and a half inactivity and again at a high HV SoC. Sounds like a different fault though.

Thanks Rolfe. That's useful

My advice is that you either trickle charge your battery to 100% yourself now and hope you can rescue it (ie: it will work as intended from now on) but my advice would be get a brand new battery, trickle charge it to100% (a NOCO trickle charger is cheap and will do a great job) note: even a brand new battery might need several hours before it is 100% charged.
This will ensure the new battery will not die within one week.

How do you know the 12v battery is at 100%? How long to trickle charge it? On the MG App it reads 12.9v

As per user manual, the car should not be stored for a long time with the HV battery at less than 50%

The intelligent battery maintenance system might decide that it’s better to not drain the HV battery and therefore might decide not to keep the 12v battery charged.

Whether the 12v battery should last a week without being charged, that very much depends on its health: even brand new batteries should be trickle charged to full before being installed. I tricked charged mine and it took a few hours more than the intelligent battery management would have charged it for to get to 100%. And 12v AGM batteries should be kept as near 100% as possible.

As per user manual, the car should not be stored for a long time with the HV battery at less than 50%

The intelligent battery maintenance system might decide that it’s better to not drain the HV battery and therefore might decide not to keep the 12v battery charged.

Whether the 12v battery should last a week without being charged, that very much depends on its health: even brand new batteries should be trickle charged to full before being installed. I tricked charged mine and it took a few hours more than the intelligent battery management would have charged it for to get to 100%. And 12v AGM batteries should be kept as near 100% as possible.

As you mention is 7 days a long time....?... in my humble opinion- No.
New cars should not shut down when many of us would travel away for one or two weeks and return expecting our new car to start up without hassle.
One of the reasons to have a new car (for me at least is that it is reliable). As for a 50% threshold!... useful to know but why such large amount of storage which will let its junior partner wither away in days! Ridiculous in my view. We all plan our EV journeys and know where and how far charging facilities are. But if you cant move, your snookered before youve started.
I appreciate your insights - better to be forewarned.

 

[MGCamb]

Reminds me of how you test whether your dog or wife loves you more. Lock them in the boot overnight and see which one is happier to see you in the morning.

 

[Lovemyev]

@drugrunner can I offer a kind word of advice, that will at least avoid any future waiting around for hours with your wife again.
Please buy yourself a 12 volt battery booster pack and keep it under the seat.
Waiting hours on end just to receive a boost from the rescue service, that takes no more than two minutes to do.

So, open the car manually with the emergency key at the driver door, pull the bonnet and connect the booster pack ( two colour coded clamps, as per the manufactures instructions ) and you will be on your way in less that five minutes.
The condition / charge state of the 12 volt battery in an EV is of more importance than a FOSSIL burning car.
You can't bump start an EV .
If you buy one, it's very likely you will never need it.
But if you DO - It's worth ever single penny of the money you have spent.
Have I got one ?.
Yes purchased it when we went full EV in 2019.
Ever used it ?.
Many times, but never on any of my EV's but it has helped out on a number of fossils !.
You know it makes sense .

 

[fnegroni]

As you mention is 7 days a long time....?... in my humble opinion- No.
New cars should not shut down when many of us would travel away for one or two weeks and return expecting our new car to start up without hassle.
One of the reasons to have a new car (for me at least is that it is reliable). As for a 50% threshold!... useful to know but why such large amount of storage which will let its junior partner wither away in days! Ridiculous in my view. We all plan our EV journeys and know where and how far charging facilities are. But if you cant move, your snookered before youve started.
I appreciate your insights - better to be forewarned.

I think your problem was compounded by the fact your 12v battery was not in a good state of health and would not keep the charge for 7 days.
The fact the car isn’t topping up your 12v made this happen faster.

One thing to highlight here:
The state of charge of a battery, especially li-ion, is not an exact science yet: below 50% charge it gets very tricky. Devices that deplete their battery rapidly like mobile phones tend to get it right more than not because they track the state of charge over time and have billions of data points.
So take that percentage number with a pinch of salt. Or lithium…

The reason it’s tricky is because voltage of a li-ion battery at 100% charge tends to drop rapidly at first, then settles for a veeeeeery long time with minimal variations and then the voltage once again rapidly falls.

 

[Ian Key]

The thing that worries me about these is that I hear they tend to die permanently if not kept charged up every couple of months. I'm likely to forget all about it. I need something that won't be ruined if I leave it untouched for a long time.

I've put a 2 monthly reoccurring reminder in my phones diary to charge the booster.

 

[Rolfe]

I've put a 2 monthly reoccurring reminder in my phones diary to charge the booster.

Highly commendable. I'm not sure I'm that organised!

One thing to highlight here:
The state of charge of a battery, especially li-ion, is not an exact science yet: below 50% charge it gets very tricky. Devices that deplete their battery rapidly like mobile phones tend to get it right more than not because they track the state of charge over time and have billions of data points.
So take that percentage number with a pinch of salt. Or lithium…

The reason it’s tricky is because voltage of a li-ion battery at 100% charge tends to drop rapidly at first, then settles for a veeeeeery long time with minimal variations and then the voltage once again rapidly falls.

That's interesting. But the car knows what the SoC display is reading. Has it no confidence in that?

More pertinently, it's absolutely true that no new car's 12v battery should be packing it in after only a week without being recharged. When I went off for 10 weeks using my Golf to get to the terminus I took a lead-acid booster pack with me to the car park. Although the car was nine, the battery was only a year or two old. I didn't need the booster pack, the car started - even though it had been sitting in the open January to March. I did need it when I got back home though - my friend's six year old Polo, which she had left in my garage, had a flat battery.

Even given that EV 12v batteries are wimpish compared to ICE car batteries, these are giving up way sooner than it would be reasonable to expect.

 

[Diggsy]

Highly commendable. I'm not sure I'm that organised!

You don’t need to be organised, the phone does that for you. Simply create a reminder and tell it how often you want reminded and that it’s a continual reminder and that’s it - the phone will remind you every time…really handy! My life would be a mess without the reminders on my phone

 

[fnegroni]

Highly commendable. I'm not sure I'm that organised!



That's interesting. But the car knows what the SoC display is reading. Has it no confidence in that?

More pertinently, it's absolutely true that no new car's 12v battery should be packing it in after only a week without being recharged. When I went off for 10 weeks using my Golf to get to the terminus I took a lead-acid booster pack with me to the car park. Although the car was nine, the battery was only a year or two old. I didn't need the booster pack, the car started - even though it had been sitting in the open January to March. I did need it when I got back home though - my friend's six year old Polo, which she had left in my garage, had a flat battery.

Even given that EV 12v batteries are wimpish compared to ICE car batteries, these are giving up way sooner than it would be reasonable to expect.

My take is that some of the 12v batteries fitted to brand new mg4’s are not in a good SoC to start with and so just ‘hang in there’ until they are allowed to die peacefully

And maybe asking the car’s status repeatedly through the app.
BTW, it might also be user error. Maybe some left their map reading lights on and those 5w bulbs can
Drain a 12v battery in matter of days.

posting for reference:

 

[Rolfe]

My take is that some of the 12v batteries fitted to brand new mg4’s are not in a good SoC to start with and so just ‘hang in there’ until they are allowed to die peacefully

And maybe asking the car’s status repeatedly through the app.
BTW, it might also be user error. Maybe some left their map reading lights on and those 5w bulbs can
Drain a 12v battery in matter of days.

I've not seen any reason to suspect that there's anything wrong with mine. However, I made a point of not even opening the app all the time I was away.

I haven't checked, but don't the reading lights go off anyway when the car is locked, even if you left them on?

posting for reference:
View attachment 20310View attachment 20311View attachment 20312View attachment 20313

Very helpful, thank you.

 

[Kithmo]

I think the interior lights go off after 30 minutes if you lock the car with them switched on manually.
I've left one on overnight with both the 4 and the ZS after faffing about in the car and had no problems, but I converted them both to LEDs.

 

[GameZone]

Just curious how much a new battery would cost? Do it have to be original from MG, because I can't seem to find any alternative.

 

[siteguru]

Pretty much any standard lead-acid battery that fits the dimensions and has equivalent standard amperage will do. (Cold Cranking Amps - CCA - are somewhat irrelevant for an EV).

 

[Lovemyev]

Just curious how much a new battery would cost? Do it have to be original from MG, because I can't seem to find any alternative.

You could try getting a quote from Tanya.
They do next day delivery in the U.K. and they are used a lot by people in the trade.
Go to the web site and use your registration number to search for a battery.
If it does not find a match, just contact them and they will find you a suitable battery.

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