Parasitic drain on 12V battery

[JohnV6]

Join the club. Mine is being replaced on the 30th

 

[Lovemyev]

Common pattern forming here me thinks .
Sounds like they have had a bad batch of faulty T boxes to me !.
Which does confirm that even new cars can have parts failures then .

 

[T1 Terry]

When a parts buyer doesn't read the fine print on the great price they managed to source a required item ..... small details like QC 1/1000 rather than 1/100. If 1 unit is tested in every batch of 1000 and it comes up to be within spec, that is taking quite a gamble that the other 999 are also be within spec .... check 10 units out of each batch of 1,000 and they all meet specs, there is fair level of confidence that batch will be mostly good

T1 Terry

 

[Joningy]

And here it is...!

MG Technical have decided the car needs the T-Box replacing!

My S5 is currently in for investigation, nothing yet heard after 3 days!

 

[emmrecs]

My S5 is currently in for investigation, nothing yet heard after 3 days!

Don't panic; it took more than a week of diagnostics for MG to finally admit the need to make this change!

 

[NickHeynes]

I'm collecting my New MGS5 in a couple of weeks should I ask my dealer about this?
What is a T box ?

 

[JohnV6]

It handle the connectivity to the web etc. When it fails the SOS call fails as does thesat nav, mg app etc

 

[Lovemyev]

My S5 is currently in for investigation, nothing yet heard after 3 days!

This is normal for MG at least.
It’s a long winded process.
They have to be authorised by MG CS to carry out their investigations, or they run the risk of not getting paid for the time.
If they need help in diagnosing the issue, they have to raise a ticket and then upload there findings of the tests they have been authorised to make.
Then wait for a responce and further instructions.
If the car needs any parts ordering, it has to be granted by them.
All this back wards and forwards takes time unfortunately and this is what makes the process so frustrating for both the dealer and especially the customer.
This way MG are in total control of the costs of any labour and parts.
It’s a similar system with other manufacturers, but the time taken is much slicker.
Of course wait times on spare parts can be lengthy, IF they are not held in the U.K. and therefore require shipping from China.
MG has said that they do intend to improve parts supply to the U.K.

 

[Joningy]

I've got my S5 back, the ONLY abnormal recorded drain was from my permanent live Viofo dash cam!

I'd inadvertently disconnected the rear camera instead of the permanent live feed, so it appears to be my fault, ok hands up if it's my mistake, I'll put it down to senility.
I hope they are correct, but what I don't understand is why the battery drain only happened in the week or so leading up to Christmas, I fitted the dash cam mid September.
I can only wait and see, but I'm not 100% confident the temporary removal of the dash cam will be a permanent fix to the battery drain.
If it does turn out to be the dash cam, I'll rewire the feed to switch from a different ignition switched fuse.

One thing this saga has taught me is that when we eventually replace my wife's Hyundai Tucson, it won't be similar to the courtesy car I ran around with for 3 days, a new 75 plate Peugeot 208 EV, in comparison, the S5 is very composed, much nicer to drive, the range on the 208 is rubbish, very jittery, even bouncy on the road.

This is normal for MG at least.
It’s a long winded process.
They have to be authorised by MG CS to carry out their investigations, or they run the risk of not getting paid for the time.
If they need help in diagnosing the issue, they have to raise a ticket and then upload there findings of the tests they have been authorised to make.
Then wait for a responce and further instructions.
If the car needs any parts ordering, it has to be granted by them.
All this back wards and forwards takes time unfortunately and this is what makes the process so frustrating for both the dealer and especially the customer.
This way MG are in total control of the costs of any labour and parts.
It’s a similar system with other manufacturers, but the time taken is much slicker.
Of course wait times on spare parts can be lengthy, IF they are not held in the U.K. and therefore require shipping from China.
MG has said that they do intend to improve parts supply to the U.K.

Interestingly on lengthy MG parts delivery times @Lovemyev , I recently ordered some unimportant S5 under centre armrest storage trays from China, (thanks @Ian Key ) less than £15 value, they arrived by DHL airmail 7 days from ordering, so why do spare parts take weeks and sometimes months to be shipped to Europe?
Sounds like a possible supply chain delay, but I can't imagine why, it's mysterious.

 

[Ian Key]

Interestingly on lengthy MG parts delivery times @Lovemyev , I recently ordered some unimportant S5 under centre armrest storage trays from China, (thanks @Ian Key ) less than £15 value, they arrived by DHL airmail 7 days from ordering, so why do spare parts take weeks and sometimes months to be shipped to Europe?
Sounds like a possible supply chain delay, but I can't imagine why, it's mysterious.

It could be that the pieces from AliExpress were already sat in a warehouse just waiting for an address label to be attached to them. The parts from MG would have to be sourced from the parts supplier, checked, packed and shipped from China.

They couldn't be taken from the production line as they will be operating a Just In Time system where everything is counted as it's used and automatically reordered.

 

[Lovemyev]

Given the distance, it is likely that parts are not shipped by demand daily either tbh.
If the parts are coming from China then they maybe sending only once a week, once every two weeks or even once a month !.
There is likely to be a “cut off point” also, if you just missed the “cut off” then your wait time is increased.
When parts where ordered for our previous ZS EV Gen2 the guy in the parts department told me, that after they have been authorised to place the order, it will take a few days before the status updates.
If it is shown as “back order” then it’s coming from China.
But you have to rely on somebody to keep checking on its progress status.
When it updates, the system will predict an estimated ETA.
Again, this needs to be monitored.
Usually the dealer will then get a message / e.mail when the items are going to arrive with them.
We required two items for our car and both ordered on the same day.
One part arrived out of the blue after two weeks, but the second item was delayed another week and then finally arrived.
So this MAY suggest it’s weekly delivery ?.
Maybe held up in customs ?.
As soon as the second part arrived MG CS called the dealer and told them to install the parts that day !.
Because they had informed the hire company to pick up the car from my house on the very same day and they did !.
Total wait time from delivering the car to the dealer by recovery service, to back on our drive fixed.
Three days short of one month.
The two parts cost less than £200 and about two hours of labour to install.
Cost of the hire car - unknown but expensive I would expect !.
I am 100% sure this is what was driving the speed of the repair by MG CS.
It’s purely not cost effective for all parties concerned and if MG did not see this coming, then they have been totally naive .

 

[Big L]

Hi guys, final update on my MGS5, after the garage having my car 4 MONTHS, all 5 faults are sorted, including the dreaded battery drain (CCU replacement)
I still have a gut feeling it wasn't the CCU, and it may been the TBox. I have read a few threads about the MG App kicking some not all out of the app saying they are logged in on another system, this happened to me. It was thought some systems were staying open on the car once the app kicked you out. This may be a total coincidence, but about 6 weeks ago my battery stopped draining, nothing at that time had been done to the car, I had been using the app to check where the car was just out of curiosity. I was sick of it kicking me out so 6 weeks ago I deleted my MG app off my phone. Now on top of my battery not draining the SOS button is now functioning, the green light is on for the first time since owning the car.
I will never know because as soon as I picked it up I sold the car, the nightmare is now over. 4 month's of unnecessary stress gone, it's a shame as I liked the car but I was not going to wait for the next problem. Thanks for all the replies to my issues, they kept me going but I must now bid you all adieu.
BIG L

 

[CarolG]

Hi, I bought a brand new MGS5 Trophy 61kWh on 8th Aug 25, on the15th Sept 25 (a month later) the 12V battery was depleted. I don't use the car with just the 12V battery running, I make sure the car is in the ready mode. The AA said I have a parasitic drain on the 12V battery. MG had the car 6 days, said they fixed it and it drained again 5 days later. It's back in with the MG garage where I purchased it from, they have had it 3 weeks and still don't have a clue. The first garage I went to said they had another MGS5 and 2 BYD's with the same problem. Has anyone else been in this situation, with a brand new car. The garage has had the car longer than I've had it on the road.
TIA.

Hi. I am having the same problem. MGS5 EV Trophy long distance, bought August 2025. 12v battery drained by mid December 2025. Told by dealer it had been replaced with a 'stronger' battery (whatever that means) and now dead again 1 month later. Note others threads on here reporting similarly so seems to be a problem although my dealer is denying being aware of a problem. Time to kick up a fuss! Carol G

 

[dx4100]

Ah what a shame you had to sell it. Good luck with whatever you get next.

 

[MG Clive]

I will never know because as soon as I picked it up I sold the car, the nightmare is now over. 4 month's of unnecessary stress gone, it's a shame as I liked the car but I was not going to wait for the next problem. Thanks for all the replies to my issues, they kept me going but I must now bid you all adieu.

That's got to be the best way to sort your car problems, get rid.

I hope your next car gives you a trouble free life @Big L

 

[Joningy]

Hi. I am having the same problem. MGS5 EV Trophy long distance, bought August 2025. 12v battery drained by mid December 2025. Told by dealer it had been replaced with a 'stronger' battery (whatever that means) and now dead again 1 month later. Note others threads on here reporting similarly so seems to be a problem although my dealer is denying being aware of a problem. Time to kick up a fuss! Carol G

Sadly you aren't alone Carol, there are quite a few moans on here, especially mine.

For the umpteenth time and 2nd today, I'd strongly advise buying an inexpensive 12 volt jump starter booster for around £30 upwards, this will get you up and running in no time, it's easy to use, but to repeat myself yet again, DO NOT keep it in the S5 boot, it's extremely difficult to access with no 12v power, under the centre console or arm rest is a popular location on here as advised by @Ian Key
If you don't think you can manage the job, someone (perhaps me) can guide you through it, it's straightforward.

It's given me a thought of producing a step by step guide, including piccy's, but I'm away for a few weeks and wont have time before I'm away.

 

[SFPlatt]

Hi, I bought a brand new MGS5 Trophy 61kWh on 8th Aug 25, on the15th Sept 25 (a month later) the 12V battery was depleted. I don't use the car with just the 12V battery running, I make sure the car is in the ready mode. The AA said I have a parasitic drain on the 12V battery. MG had the car 6 days, said they fixed it and it drained again 5 days later. It's back in with the MG garage where I purchased it from, they have had it 3 weeks and still don't have a clue. The first garage I went to said they had another MGS5 and 2 BYD's with the same problem. Has anyone else been in this situation, with a brand new car. The garage has had the car longer than I've had it on the road.
TIA.

Hi I have read your comments and many others here that clearly indicate there are issues. Mine has had a number of problems relating to the the 12 volt battery, and this appears to affect our model and others. There are some great comments from others which show how to do simple checks with a Multimetre. However others have had to buy Jump Starter Power Packs to save waiting for the AA which would have worked for me last week, which is ridiculous. More of a concern is that dealers cannot resolve this or try to suggest it is a "one off" issue. I have mine booked in the week after next and I will post the findings on here. The dealer here wanting £150.00 for the diagnostic, so going to have some fun understanding why I should have to pay this for a car under twelve months old.

 

[Joningy]

Nobody with a new car should NEED to buy a 12v starter pack!

But as so many manufacturers do have battery issues, it's the route me and many have taken. WTF are we supposed to do about it?

I know first hand how long it takes to get help when it's needed, so a small investment has eventually paid off for me.

Last May, I lost my MG4 car key whilst on holiday, I had to pay for a taxi home and return, pick up the spare key, Bournemouth airport to Near Andover, bargain at £140 return, one rather opportunist and greedy taxi driver wanted £400, fortunately the guy I used was very fair.

 

[emmrecs]

The dealer here wanting £150.00 for the diagnostic,

You need to fight this!!

As others have said, there should never be a question of being charged to attempt to diagnose a fault with a new car! I'm also in the "same boat" (12v battery going flat) and my local garage has now had my car for two separate diagnostic sessions, the first 2 days, the second one week, and there has never been any suggestion of me being charged. The technician who carried out the diagnostics has also been very proactive in contacting MG UK on several occasions to try to resolve the issue.

As of now, MG has agreed to supply a replacement T-Box, which the garage will fit, again at no charge whatsoever to me!

 

[SFPlatt]

Sadly you aren't alone Carol, there are quite a few moans on here, especially mine.

For the umpteenth time and 2nd today, I'd strongly advise buying an inexpensive 12 volt jump starter booster for around £30 upwards, this will get you up and running in no time, it's easy to use, but to repeat myself yet again, DO NOT keep it in the S5 boot, it's extremely difficult to access with no 12v power, under the centre console or arm rest is a popular location on here as advised by @Ian Key
If you don't think you can manage the job, someone (perhaps me) can guide you through it, it's straightforward.

It's given me a thought of producing a step by step guide, including piccy's, but I'm away for a few weeks and wont have time before I'm away.

Hi like you I have had similar issues and there are others with the same. It is stupid that like you people are having to consider boosters to get running again. I was in Devon last Tuesday, and the issue ocurred with a low battery warning. Two hours from home late at night, I did manage to get going but otherwise I would have been in the pitch dark waiting for the AA. At least I do know how to get into the car but still wouldn't have been able to start it.