Parasitic drain on 12V battery

[Slipstream]

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 .

You can check the battery condition on the I smart app.

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.

Surely you can reject the car seems to me it's not fit for purpose.

 

[NLMGSAN]

You can check the battery condition on the I smart app.

After some time, the MG goes into a deep sleep mode. So, if you want to know the battery status, most likely the connection has already been lost.

 

[mrg9999]

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.
TIA.

2022 MG ZS EV does this. I schedule automatic turn on fan (using HA) and that triggers a battery charge. I often do this a few times a day.

 

[micktreviss]

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.

I bought my MG S5 at the beginning of July, it’s a LR Trophy and I had to call MG assist about 2 weeks ago as I couldn’t unlock the car. AA pitched up and put some jumper leads on the 12V battery and I was able to sit on the seat to get it in READY mode.
He suggested that the 12V battery was low and not to be expected from a new battery.
Having now gained the knowledge of a) how to get into the car (blade now firmly connected to my key ring) and b) what to do to get it in READY mode (jump starter mini box from Amazon), I feel much more confident with the car.
The car is booked in for this Thursday and a battery discharge test will be the minimum.
VERY disappointed that things like this should happen, especially as the 12V battery has a huge role to play in allowing the start/ready process!!

 

[5teep]

I bought my MG S5 at the beginning of July, it’s a LR Trophy and I had to call MG assist about 2 weeks ago as I couldn’t unlock the car. AA pitched up and put some jumper leads on the 12v battery and I was able to sit on the seat to get it in READY mode.
He suggested that the 12v battery was low and not to be expected from a new battery.
Having now gained the knowledge of a) how to get into the car (blade now firmly connected to my key ring) and b) what to do to get it in READY mode (jump starter mini box from Amazon), I feel much more confident with the car.
The car is booked in for this Thursday and a battery discharge test will be the minimum.
VERY disappointed that things like this should happen, especially as the 12v battery has a huge role to play in allowing the start/ready process!!

12V battery issues are common to all EVs (though one failing this quickly is unusual). There was talk on the forum a couple of years ago about using a leisure battery instead but I don't know if anyone ever tried.

 

[nicknick44]

I’ve got a 74 plate Zs Ev that has a problem with draining battery. Dealer has been told and tried to fix it along with other faults but they haven’t got a clue. I’m now in talks with finance company about rejecting car

 

[keithw64]

A common problem with the MG5 was an error message saying.'Radio Module Disconnected' (or something similar as I don't have the car now) and that caused a drain on the 12v system enough to flatten the battery over night. Happened to me a couple of times just before I PXed the car for my MGS5. Don't know if the S has a similar module but doesn't display the error. Was your radio working ok just before it happened?

 

[ANDREW101]

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.

Mine often comes up with low battery warning but when check actual reading it's fine. Bit weird hut not as annoying as discharged!

 

[5teep]

Mine often comes up with low battery warning but when check actual reading it's fine. Bit weird hut not as annoying as discharged!

If you watch carefully when you first turn the car on you'll see the 12V battery starts low and climbs to 13.9(ish) as the HV battery kicks in to feed power to it.

 

[noel72]

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.

You can reject the car under the consumer act 2015 ,within 30 days, or they get 1 chance to fix it. That is the law.

 

[Coulomb]

AA pitched up and put some jumper leads on the 12V battery and I was able to sit on the seat to get it in READY mode.

In the MG4 at least, merely sitting on the seat turns the car on, but not yet into ready mode until/unless the brake pedal is pressed. When the car is on but not ready, the 12V battery is being charged, and HVAC is available. But the car can't be put into Drive or Reverse, so there is no chance of it accidentally moving under its own power.

 

[Ozzie]

My ZS E is a 71 reg and when the 12 v battery failed after two years I had it replaced with a better unit as both the AA and MG dealer said the 12v batteries fitted by MG were not good. They also informed me the 12v is only charged from the traction battery when the car is switched on.
After less than twelve months I started to received screen warnings that the 12v battery was low. This was after a 100 mile trip. When these warnings continued I returned to the MG dealer who performed the above drain tests and eventually conceded it was the battery which they replaced under warranty.
As a qualified electronics and computer engineer I have also performed drain test myself without success.
I suspect there is an intermittent bug which very occasionally leaves something powered up when the vehicle is switched off.
I now carry a booster pack and tools to enable me to access the bonnet release to then "Jump" start the vehicle.
Talking with AA and other auto electricians I understand this problem is not limited to EVs.
I'm sorry I can't yet provide an answer, but Big L, you are not alone.

 

[Forest4Ever]

I have exactly the same problem. Ripping my hair out. Drove 60 miles in daylight yesterday morning in good weather conditions and no activity on in car. Drove home in dark later in day and battery went flat. I had a lot of activity in the car coming back, footy on radio, sat nav on, 1 seat heater on etc. There is clearly a fault here somewhere that unfortunately is common with the MGS5. I need to check now the Ampage of the battery installed but it is does sound like a parasitic drain and sounds like I am going to have the same problems as you are experiencing. I assume I can recharge my existing battery by attaching to a charger whilst it is located in the front boot ?

There are batteries around apparently that hold 400A rather than the weak 32A batteries they fit on manufacture but i need to check it IS indeed a 32A fitted. I'll check.

 

[David MG]

I had a similar problem with my Kia Nero, it just keep draining the 12 volt battery. I did notice after I had charged up the battery there was a small spark when re-connecting it and a noise from the rear of the car. After a battery change and a couple of visits to the service bay, they finally changed the boot switch, this resolved the problem.

 

[LenEV2016]

I have exactly the same problem. Ripping my hair out. Drove 60 miles in daylight yesterday morning in good weather conditions and no activity on in car. Drove home in dark later in day and battery went flat. I had a lot of activity in the car coming back, footy on radio, sat nav on, 1 seat heater on etc. There is clearly a fault here somewhere that unfortunately is common with the MGS5. I need to check now the Ampage of the battery installed but it is does sound like a parasitic drain and sounds like I am going to have the same problems as you are experiencing. I assume I can recharge my existing battery by attaching to a charger whilst it is located in the front boot ?

There are batteries around apparently that hold 400A rather than the weak 32A batteries they fit on manufacture but i need to check it IS indeed a 32A fitted. I'll check.

This was/is an issue with some MG4s also, not sure if it has been mentioned but some 4s battery cables were loose from transit and hadn't been tightened during pdi checks.

Add that to not the best quality battery and they were failing, faulty boot switches seem a common cause on a few makes of car, definitely worth investigating

 

[Joningy]

This was/is an issue with some MG4s also, not sure if it has been mentioned but some 4s battery cables were loose from transit and hadn't been tightened during pdi checks.

Add that to not the best quality battery and they were failing, faulty boot switches seem a common cause on a few makes of car, definitely worth investigating

What effing PDI checks? I'm convinced MG's don't get a PDI check, just a quick clean from a low paid foreign worker, it's probably another way to save a few quid!

 

[LenEV2016]

What effing PDI checks? I'm convinced MG's don't get a PDI check, just a quick clean from a low paid foreign worker, it's probably another way to save a few quid!

Don't disagree; they should check everything, including all the software updates, but we know from this forum there have been far too many reports of stuff being missed.