Parasitic drain on 12V battery

[Big L]

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.

 

[5teep]

I understood that the main battery is meant to kick in and charge the 12V battery when it drops even if the car is 'off'. It seems yours is not doing that so maybe there's a faulty sensor somewhere? There's always going to be some drain on the 12V battery which is why the main one is meant to charge it.

 

[Big L]

Yeah that's correct, it has a parasitic drain but in 4 weeks the garage are still no further forward. They basically wiped the car and put new updates in and it still didn't work. I'm hoping I find someone with the same issue and how it was fixed.

 

[Lovemyev]

It goes without saying that you don't have a dash cam etc installed of course ?.
The dealer needs to enlist the help of a a good auto electrician, who can locate which system on the car is constantly pulling the draw / drain.
This is normally achieved by connecting an amp clamp to one terminal of the battery, then by following a process of elimination, each fuses or relay is removed.
When the current then drops to zero, this is circuit pulling current when it should not be.
The diagnostic equipment is unable to identify / perform this task of course.
Without been able to correctly locate the source of the drain correctly, then I don't how they intend to resolve the problem tbh ?.
Not want you want to hear of course, but I cant see a way forward otherwise ?.

​

 

[Big L]

Yeah, no dash cam. I've told the garage it needs a auto electrician but all they do is ring MG and they tell them to try different things. It's annoying as I have only had it a month, but garage said I can't reject it and get a refund as they haven't had a chance to repair it. What's even more annoying there's a boot fault as well that they haven't managed to fix neither.

 

[MG Clive]

Welcome to MGEVs @Big L, I hope you manage to get this sorted, please keep us informed.

 

[Big L]

Will do

 

[Alb]

It would be worthwhile if you fitted a Bluetooth battery monitor.

 

[Big L]

I was thinking of that but it pains me to do it when the car is only 2 months old. Luckily I bought a jump starter which was invaluable, again I shouldn't have to do this. I wish the MG app (which is rubbish by the way) had the 12V battery monitoring on that.

 

[Lovemyev]

What's even more annoying there's a boot fault as well that they haven't managed to fix neither.

Oh….. Interesting .
Could these two problems be liked in some way ?.
The boot has an electric latching system and has powered opening ?.
Of course, they have replaced the 12 volt with another one to be 100% sure it’s not the battery itself ???!?.

 

[Big L]

I have already mentioned the boot could be the cause. No they have not replaced the 12V battery, so now it has been depleted 3 times and been recharged. Me personally I would have put a new battery on but they don't listen.

 

[5teep]

I have already mentioned the boot could be the cause. No they have not replaced the 12v battery, so now it has been depleted 3 times and been recharged. Me personally I would have put a new battery on but they don't listen.

Problem for dealers is they have to prove to MG a part is faulty and get their approval before they can swap it out. The 12V battery is easy though, just charge it, leave disconnected from the car and see if it will hold a charge.

 

[Big L]

, I was going to ask them to put a new one on regardless, even if it means I buy the battery, just for peace of mind.

 

[Lovemyev]

Surely for there on peace of mind, you think they would just pop on a battery from another car for a couple of days ?.
Takes less than 5 minutes and has no cost associated to it.

 

[Big L]

You would think so but they are the experts .
I will mention it in Monday but don't hold out much hope.

 

[Lovemyev]

Has the dealer or MG themselves given you a car to use ?.

 

[Big L]

1st time no, but second garage gave me a car, it's mine until they sort this out. It's a petrol hybrid but at least it's wheels.

 

[asti1488]

Hi sorry for your issues, I haven't got my car yet but have ordered a wireless battery monitor so I can see the battery condition and hopefully get a bit of early warning if an issue shows. My neighbour had to call the AA as one day he couldn't unlock his car as the 12V battery had drained .

 

[Big L]

I was thinking of doing that but I shouldn't have to do that on a 25 plate car that's 2 months old.

 

[asti1488]

Yes that's true, the monitor would just give a bit of early warning so you could at least always start the car and maybe see how fast the battery was draining