ZS EV 12v battery issue

KrispiiDuck

Standard Member
Joined
Oct 2, 2024
Messages
17
Reaction score
8
Points
7
Location
Oxfordshire, England
Driving
ZS EV
Hi folks,

Interested in your opinions please.

My 74 plate ZS EV Trophy turned into a large blue paperweight yesterday. None of the keys worked for unlocking and eventually I made it into the cabin using the emergency blade key. The dashboard was dead - no light, not able to start. I called upon MG Assist. AA were out within the hour and diagnosed the 12v battery being shot - he said that it was only taking 5 rather than up to 65 amps? (image from the AA breakdown report attached) So the patrol guy used a booster pack to get the car started and told me to take it to the garage as the car is under warranty - he also hooked me up with a hire car.

I drove to the dealer and booked the car in, sent them the battery report and left the car with them, expecting to get the battery replaced.

This afternoon I got a call to say that it started fine this morning and they are blaming my dashcam (which incidentally was fitted months ago and we left it home alone for 3 weeks in April and no issues when we returned. They are going to test it again tomorrow, but it sounds as though they are saying that there is no fault and they will not be replacing the battery.
 

Attachments

  • unnamed (2).webp
    unnamed (2).webp
    25.1 KB · Views: 33
The 12V battery has a 12 month warranty on it, so I suppose see how it goes and at the slightest sign of not holding its charge, get it swapped out.
 
Recently did a bit of research on dash cams. Are you using the parking mode (meaning the dash cam stays on even when the car is off and parked), assuming it is hardwired and supports that? If so the hardwire kit should have a safety cutoff at a certain voltage, usually there are a few different options. Mind telling us which dash cam it is?

From what (little) I understand, lead acid batteries do NOT like being deeply discharged and can take damage from it, especially if done repeatedly. Could be that the low charge rate the AA guy saw had something to do with the 0% SOC of the battery and that the amps would increase once it has charged a bit. I suspect the dealership charged the battery overnight so it looks ok on a quick test - doesn't mean the battery is actually healthy though.

Also if someone can explain this "74 plate" thing to me I'd appreciate it. Seen different variants of it on this forum and it only seems to be a thing in the UK?
 
Recently did a bit of research on dash cams. Are you using the parking mode (meaning the dash cam stays on even when the car is off and parked), assuming it is hardwired and supports that? If so the hardwire kit should have a safety cutoff at a certain voltage, usually there are a few different options. Mind telling us which dash cam it is?

From what (little) I understand, lead acid batteries do NOT like being deeply discharged and can take damage from it, especially if done repeatedly. Could be that the low charge rate the AA guy saw had something to do with the 0% SOC of the battery and that the amps would increase once it has charged a bit. I suspect the dealership charged the battery overnight so it looks ok on a quick test - doesn't mean the battery is actually healthy though.

Also if someone can explain this "74 plate" thing to me I'd appreciate it. Seen different variants of it on this forum and it only seems to be a thing in the UK?
It is a Thinkware F200, hardwired and does support recording when the car is turned off, set at the lowest reording level, but the car was only standing over a weekend - previously I had left it for 3 weeks when we were away earlier this year with no issues on our return. I've had to collect the car as is and will keep an eye on it, but they said to get it recovered to them without jumpstarting it if it happens again.

74 plate refers to when the car was registered in the UK - we have two registration periods in a year.
March to August 2025 would be a 25 plate, mine was registered in September 2024, so it is a 74 plate. Hope that helps!
 
It is a Thinkware F200, hardwired and does support recording when the car is turned off, set at the lowest reording level, but the car was only standing over a weekend - previously I had left it for 3 weeks when we were away earlier this year with no issues on our return. I've had to collect the car as is and will keep an eye on it, but they said to get it recovered to them without jumpstarting it if it happens again.

74 plate refers to when the car was registered in the UK - we have two registration periods in a year.
March to August 2025 would be a 25 plate, mine was registered in September 2024, so it is a 74 plate. Hope that helps!
Ok I haven't heard of that dash cam, but I would check if the hardwire kit has that safety cutoff and what it's set to. Basically the lower voltage settings are not recommended to preserve battery health. If it doesn't have that cutoff feature then your dash cam might have caused damage to your battery over the long term and it's just become noticeable now that the battery health has degraded.

Thanks for explaining the plate thing and sorry if I'm being daft, but how does September 24 translate to the number 74? Edit: Is Sep-Feb just always 7 and Mar-Aug 2 and then the second digit is the year? Guess I could Google this, sorry 😄.
 
Last edited:
I'll have a chat with my auto-electrician regarding the dashcam.

As far as the registration dates go, I think it was an arbitrary decision to offset the later registrations by 50, way back in 2000.

More info:

Registration plates in the United Kingdom follow a specific format and set of rules, which makes it simple to work out the age of a car or van.

Standard UK car number plates consist of a combination of letters and numbers, typically in the format of two letters, followed by two numbers, a space, and then three more letters or numbers (for example, AB12 CDU).

What do the letters and numbers on a UK registration plate mean?

  • The first two letters represent the region where the vehicle was registered and are assigned by the Driver and Vehicle Licensing Agency (DVLA)
  • The two numbers in the middle are the ‘age identifier’. The second number indicates the year of registration, and the first number indicates the specific six-month period within that year (usually March to August or September to February).
  • The last three letters on the plate are generally random and do not carry any specific information
 
Thanks for explaining the plate thing and sorry if I'm being daft, but how does September 24 translate to the number 74? Edit: Is Sep-Feb just always 7 and Mar-Aug 2 and then the second digit is the year? Guess I could Google this, sorry 😄.

😂 Google says:
"In the UK, new car registration plates are released twice a year, in March and September. The two numbers in the middle of the plate indicate the age of the vehicle and change with each release. For example, in March 2025, the age identifier will be "25", and in September 2025, it will be "75".

so for 2025 registered cars you will have 74 until March, then 25 until September when it turns 75 😂
 
😂 Google says:
"In the UK, new car registration plates are released twice a year, in March and September. The two numbers in the middle of the plate indicate the age of the vehicle and change with each release. For example, in March 2025, the age identifier will be "25", and in September 2025, it will be "75".

so for 2025 registered cars you will have 74 until March, then 25 until September when it turns 75 😂
Odd. Especially as you can't tell the decades apart, so what's the point? Maybe there are more magic numbers I don't know about. Anyway, at least I have an idea now, thanks. I think I must just stop trying to understand it fully and/or blame my current COVID infection...
 
Odd. Especially as you can't tell the decades apart, so what's the point? Maybe there are more magic numbers I don't know about. Anyway, at least I have an idea now, thanks. I think I must just stop trying to understand it fully and/or blame my current COVID infection...
I don't understand the logic either but as with many other things, "hurts less if I don't think about it ..."
😷 Hope you get well soon!
 
They started with the silly registration plates many years ago to help the struggling British car industry. It all started with an 'A' at the end of the number I had a 'D' which was first registered in 1966. Then as new car sales started to go down the car manufacturers (Mainly BMC) persuaded the government to bring in twice yearly registrations to persuade the show off's to go 'one up' on the rest of the poorer population with a new car.
Nothing has changed to the extent that manufacturers produce 'Facelift models' so the idiots will have to have the latest 'design', like buying a new tee-shirt.
 
If you dont need the camera to film while parked up, there is an excellent USB socket on the side of the plastic housing, that covers the cameras at the top of the front windscreen.

It's very close to the windscreen on the one side (right side here, but maybe left, as you drive in the wrong side of the road over there ;) )

My Dashcam is connected there, this USB turns off with the "ignition" and thus it will be incapable of draining the 12V battery.

Also, depending on the state of your software, someone claimed that then car will now enable the high voltage battery, to charge the 12V battery when the car is off for an extended period of time and the logs i have, from when we went on vacation and had it parked up for 16 days, actually seem to confirm that.

I have attached the voltage readings of the 12V battery

We went away on July 11, the spike on July 13 is a mobile window rockchip repairman that was in the car, fixing a small rock strike.

After that the voltage dropped until the 19'th where we were not at home, but the car seems to have charged the battery.

Strange thing is...It still went into deep sleep to prevent the 12V battery being depleted on July 21, but that would not be needed if the car tops off the 12V battery anyway.

mgbat.webp
 
[...] car will now enable the high voltage battery, to charge the 12V battery when the car is off for an extended period of time and the logs i have, from when we went on vacation and had it parked up for 16 days, actually seem to confirm that.

Strange thing is...It still went into deep sleep to prevent the 12V battery being depleted on July 21, but that would not be needed if the car tops off the 12V battery anyway.
That's cool that it does that now! And yeah, it's annoying when it goes into deep sleep. Sometimes even taking it for a short drive isn't enough to get the iSmart app to work again. Ideally it would wake up if you do something via the app, but I guess the relevant hardware isn't capable of going into a kind of low power stand-by mode.
 
That's cool that it does that now! And yeah, it's annoying when it goes into deep sleep. Sometimes even taking it for a short drive isn't enough to get the iSmart app to work again. Ideally it would wake up if you do something via the app, but I guess the relevant hardware isn't capable of going into a kind of low power stand-by mode.
Yes, the app even says that it can not contact the car and that this might be because it is in a deep sleep to preserve the 12V battery and to just put the car into Ready state for it to wake up.

I fully understand the need for deep sleep from when the car did not top up the battery, but now that it does, it's kind of redundant, especially since it seems it will only need to charge the battery about every ~week, if my graph is a true representation of what it does and when.
 
On my 71 Plate ZS EV the original 12v battery failed. It was replaced and just over 12 months later I had to call the AA as the battery was flat.
Dealer ran a 12 hour leakage test and then diagnosed battery and gave a good discount on a high spec replacement.
The car is in my garage, locked and charge cable disconnected yet I have twice had a message "12v low, do not park for more than three days."
It recently has failed again.
Any suggestions please?
PS I was advised not to use the MG App but is that how the above 12v voltage trace was obtained?
 
We only use our 2023 SR Trophy ZS EV about three times a week & this battery gave up the ghost at 1500 miles :eek: of course as s0ds law goes it was just out of warranty. :mad:
 
I have the MG5 but my wife has the ZS long Range.
I may have found the underlying problem to this as I have also had the dreaded (do not leave your car parked for 3 days) then the dead battery 3 times, and 3 times Arnold Clark MG have said they have fixed it. They've changed the battery, and also changed a 'faulty' sensor.
Following those fixes we still have ACC failure, airbag failure etc etc as well as, yes you guessed it, "do not leave your car parked for 3 days".

Anyhow. Whilst sat in the car, taking pictures of the latest warning message with the car off, I noticed that it continually turns the handbrake on and off, and that the Media screen turns on briefly, then turns off again. Now if this is happening all day and night, surely that could be contributing to the 12V battery drain and subsequent failure in an unusually short time. I've messaged Arnold Clark to take the vehicle back and I'll see what they say. If I find the video/images I'll post them here too.,
 
Support us by becoming a Premium Member

Latest MG EVs video

First Look: MG IM5 & IM6 – Premium EV Saloon & SUV Unveiled at Goodwood!
Subscribe to our YouTube channel
Back
Top Bottom