MG4 Urban 12V Battery Issue

[jay273]

Hi, to everyone here, I am a new owner of an MG4 Urban Premium Long Range for the past two weeks and loving the car, but ran into a problem after being away from the car for 1 week on holiday. When I got back the car was totally dead, after getting into the car old school way via emergency key popped the bonnet and confirmed the 12V battery was dead, did an overnight charge but in the morning battery still dead.

Things of note.

• whilst away kept an eye on the car via app.
• 1st day away car HV charge was 30%
• Last app update day before my return HV charge at 22%.
• When charging the 12V battery noticed indicators intermittently blinking.

Just wondering if anyone else has had similar issues?
Planning on getting car back to dealer on Tuesday after bank holiday to diagnose (hoping its as simple as a dodgy 12V battery that just needs to be replaced).

 

[Slipstream]

Hi, to everyone here, I am a new owner of an MG4 Urban Premium Long Range for the past two weeks and loving the car, but ran into a problem after being away from the car for 1 week on holiday. When I got back the car was totally dead, after getting into the car old school way via emergency key popped the bonnet and confirmed the 12v battery was dead, did an overnight charge but in the morning battery still dead.

Things of note.

• whilst away kept an eye on the car via app.
• 1st day away car HV charge was 30%
• Last app update day before my return HV charge at 22%.
• When charging the 12v battery noticed indicators intermittently blinking.

Just wondering if anyone else has had similar issues?
Planning on getting car back to dealer on Tuesday after bank holiday to diagnose (hoping its as simple as a dodgy 12v battery that just needs to be replaced).

Not sure if this will help. But a few owners on here who have had battery problems have found the battery terminals to be loose worth checking ?

 

[jay273]

Hi, checked the terminals, all are tight, car heading to dealers on Friday for some diagnostics, will report back what they find

 

[jay273]

Should also add that got the car running enough to charge the HV to 100% using a NOCO Boost GBX45 Jump Starter(this will be in the car now for its life, even if the dealer fixes the issue). 12V battery lasted at least for 16 hours, but woke up the next morning to another dead car.

 

[fnegroni]

Hi, to everyone here, I am a new owner of an MG4 Urban Premium Long Range for the past two weeks and loving the car, but ran into a problem after being away from the car for 1 week on holiday. When I got back the car was totally dead, after getting into the car old school way via emergency key popped the bonnet and confirmed the 12v battery was dead, did an overnight charge but in the morning battery still dead.

Things of note.

• whilst away kept an eye on the car via app.
• 1st day away car HV charge was 30%
• Last app update day before my return HV charge at 22%.
• When charging the 12v battery noticed indicators intermittently blinking.

Just wondering if anyone else has had similar issues?
Planning on getting car back to dealer on Tuesday after bank holiday to diagnose (hoping its as simple as a dodgy 12v battery that just needs to be replaced).

for future reference, bear in mind the 12V battery might not be charged while the car is switched off if the HV battery state of charge is below 50%

And the battery charge going from 30% to 22% in one week seems excessive to me.
i've actually never seen the battery charge depleting while away on holiday over the years.

 

[fnegroni]

Should also add that got the car running enough to charge the HV to 100% using a NOCO Boost GBX45 Jump Starter(this will be in the car now for its life, even if the dealer fixes the issue). 12v battery lasted at least for 16 hours, but woke up the next morning to another dead car.

Once the 12V battery is fully depleted, you need to rescue it using a charger like the NOCO genius 2 to push some charge into it and then keep charging to 100% which can take a day or more

 

[tsedge]

Normal behaviour should be zero or 1% loss of the HV battery per week.

Suggests there is a phantom drain somewhere which is causing the problem.

I'd recommend having the dealer apply all available software updates and checking for faulty modules.

I'm assuming you have nothing plugged into the car that could drain the 12V battery?

 

[jay273]

once the 12v battery is fully depleted, you need to rescue it using a charger like the NOCO genius 2 to push some charge into it and then keep charging to 100% which can take a day or more

Yeah I did think I read that somewhere, but unfortunately even with HV at 100% issue repeated itself next day. Plus after the initial problem left the 12V battery connected to a NOCO Genius10 overnight but woke up still to a dead battery, did not disconnect the battery from the car so if there is a phantom drain somewhere maybe this killed the charge?

 

[CrazyDriver08]

From my experience, it’s usually not the HV battery itself, but the 12V system not being properly maintained while the car is parked. The MG4 seems to be a bit sensitive if it sits for days, especially with low HV state or app activity waking the car up.

The blinking indicators while charging also sounds like the 12V battery was heavily discharged.

 

[TonyCorbett16]

It’s still safer to carry a spare 12V battery.

 

[William100]

Had the same problem with my MG4 xpower and had to call the AA, the engineer said that they have found the chinese 12volt batteries were poor and suggested I fitted a Bosch battery which I did and have not had any problems for 2 years, infomed my dealer and they refunded the cost

 

[Kevin Smith]

If you have had the car for less than 30 days you can reject the car for a full refund and start again buying something else but if you keep it past 30 days you will have all the hassle of a faulty car and a dealer network that is sometimes found wanting... not saying you should but I wouldn't let them drag it out nor accept that the 12V battery is a disposable and uncovered by warranty - it's consumer protection act 2015 that matters here - faulty goods.

 

[DennyRefor06]

f your HV (High Voltage) battery dropped from 30% to 22% while parked, the car was likely trying to top up the 12V rail but failing due to a parasitic draw or a faulty cell.
Since an overnight charge didn't wake it up, the internal resistance is probably too high for the BMS to accept a charge.
Definitely push the dealer for a full health check; these EFB/AGM units can be finicky if they've sat at low voltage for too long

 

[jay273]

The problem appears to be solved
Thanks to everyone who left comments on this thread.
However going to run though everything including the root cause just in case it helps others...

The car went to the MG dealer for some diagnostics...

• Battery test = OK
• Parasitic drain test = OK
• However the next morning woke up again to a dead car :-(

Then I started to research a lot more, the outcome could not find anyone else having the same issue with the 12v battery dying so frequently on an Urban even after jump starting and doing a full over-night charge.

We have an EO Mini Pro3 Charger and me being me, hooked the iSmart App (using a dedicated account to avoid my and my wife's apps from being logged out) to the chargers ev.energy app for smart charging.

By luck i decided to look at the ev.energy app for a little while and noticed the last vehicle check-in was always about 10 minutes ago. Lightbulb moment and with a little AI help to confirm my theory.

If the ev.energy system was polling iSmart every 10 minutes the T-Box would constantly be getting woke up causing a small 0.02 Amp drain and not let the car go into a deep sleep which could explain the small 12v 35Amp/hr battery in the Urban getting run down when it was parked up for a short duration (1-3 days).

So I disconnected the ev.energy app from iSmart and switched my charger to dumb mode.

5 days later I have a car that hasn't needed to be used but still works.
Also the HV charge has stayed steady at 100% for the same time.

The lessons I have learnt from this...

1. Don't connect third party systems to your car's app without checking it won't poll it like a madman.
2. If you own an EV carry a good jump starter with you just in case, who knew how important the little 12v battery is for your EV to function.
3. MG Dealers are fine and proactive when selling you car less so when you have a problem with a two week old car, even when you threaten them with a return and full refund demand under the Consumer Rights Act - Richmond MG Southampton.
4. The MG4 Urban is a very cool car, so am glad I could identify the issue even if it was self inflicted and a return was not needed.

 

[fnegroni]

glad you found the root cause

 

[siteguru]

BTW, it's the Consumer Rights Act, not Credit.

 

[jay273]

BTW, it's the Consumer Rights Act, not Credit.

whoops, thanks, updated

 

[siteguru]

Still one Consumer too many.