MG4 won't unlock or start 10 hours after last use

[mxtthewf]

Hi,

Firstly apologies if this thread is a duplicate or in the wrong place,

So I drove my MG4 home from work this morning around 9 AM and put it on charge as the battery was around 30%. I've then just gone to the car and its completely dead, both keys won't work to unlock the vehicle, tried the manual key and that's not doing anything either. The charger is stuck in the vehicle and no lights are showing.

I've rung MG Assistance and they are telling me they are 3 hours out, and it could be due to a flat battery or a loose wire (apparently a problem they are seeing in this model). I don't think anything was left on, but I did check the app to make sure it was charging earlier today.

Has anyone else experienced similar problems?

I got this car brand new in March '23, and I've loved it. But this is the sort of thing that makes you lose confidence in a car, not knowing if it'll start when you go to get in it, which is so frustrating given that its a brand new vehicle that's only 6 months old.

Any advice would be greatly appreciated,
Thanks

 

[PristDean]

Dead 12v battery. This sounds to me (as you had the car on charge) like once you have it back up and running, take it back to your dealer and ensure the BMS (battery management system) and other module firmware is up to date. Potentially loose battery connection too, should be checked.
The 12v battery should charge itself up from the HV battery when the car is on charge or the HV battery over 20%, seems yours did not.
If you have a 12v battery charger, disconnect the 12v battery and charge it, then reconnect.

 

[Rolfe]

Have you been unable to get into the car at all? You should be able to open it with the manual key even if it's completely dead.



It sounds like a flat 12v battery, and there are a (confusing) number of threads about this issue. The bottom line is that if you can get the bonnet open and some sort of jump-start leads to the terminals of the 12v, the car should start.

If you can get into the car with the manual key, you can then release the latch on the bonnet and lift it. Check the terminals on the 12v battery and if anything is loose, tighten it. If you have a car-starter battery kit, either Li-ion or lead-acid, then clipping that on to the 12v terminals should wake the car up. The car will then charge the 12v up from the traction battery. As a last resort, you can use the 12v battery of any handy ICE car in just the same way as you would use it to jump-start another ICE car with a flat battery. (While you should never use an EV's 12v to jump-start an ICE car, it might be possible to use another EV to jump-start an EV, but don't quote me on that.)

Try it if you can and good luck.

Of course the next question after that is, why did it happen? That's trickier.

Oops, gazumped by PristDean.

 

[stevegus]

I discovered after 2 weeks of ownership when looking around under the bonnet that the neg lead was just pushed on loose to the battery post. Not tightened at all.

 

[Rolfe]

It's a shame @mxtthewf didn't come back after the OP. I'd have liked to know how he got on. Sounds like an absolute nightmare.