That good ol' keeping the 12V battery perky thread repeat.

[Tuareg]

Have you had any additional electrical devices (alarms, hifi, lights etc) or modifications to the car?

 

[jon0881]

Make sure you had the SW upgrade to fix monitoring of the 12V system. Mine was effected by this and broke down. I was informed that if the battery does not recover i would be liable to pay for the replacement.

 

[pecker]

Make sure you had the SW upgrade to fix monitoring of the 12v system. Mine was effected by this and broke down. I was informed that if the battery does not recover i would be liable to pay for the replacement.

When was the update released, when was yours done ?

Thanks

 

[jon0881]

mine was done after a breakdown in December and they said it had 3 SW recalls outstanding. Nice for someone to contact me about it!

the update wasnt specifically for that but it was on the bugfix list for a module update and been fine since

 

[siteguru]

There's that word again - recall. There has only been one recall on the MG4 (for the locking in fix); everything else is a service campaign item. Dealers are just lazy and call them recalls, but they're not.

 

[Kithmo]

Thanks for that.
Also, climbing out of the car drops it out of Ready mode ?, so no nipping in for a cuppa for half an hour while it goes through the Ready/charge cycle as per p.289 of the manual. Guess I'll just have to go for a drive then ??

It doesn't have to be in Ready mode with the MG4, as soon as it powers up it's charging the 12V, so go get your cuppa. ?

 

[jon0881]

There's that word again - recall. There has only been one recall on the MG4 (for the locking in fix); everything else is a service campaign item. Dealers are just lazy and call them recalls, but they're not.

Actually thats a very good point. The arrogant lady on reception used recall and i said well why wasnt i contacted, she said its the DVLA that does that not us, take it with them. I checked and no logged 'recalls' for my car (lock in recall done).

 

[Rolfe]

The 12v battery charges when the big battery is charging from the mains. It also charges when moving. It does not start when unplugged and turned off.

After 1 week away at an airport car park my mg4 12v battery was flat.

What was the SoC of your HV battery at the time?

 

[Tarka]

As I have posted elsewhere the main battery will charge the 12V battery without the car being in ready mode or charging.
Here is a screenshot showing mine being charged. The car hasn't been unlocked or put on charge for over 48 hours.
View attachment 24608

Hi Ian, I have a Nov 2022 MG4 Trophy (bought at 15mths old, possibly ex-demo so had some teething issues). My 12V battery went flat after a week away in March 2024 then again after 2 weeks away Sept 2025 (this time it had to be replaced). I have a number of questions!:
1. How are you telling from the app that the 12V battery is charging from the main battery when the car is powered off and left? Is it just that the voltage is maintained over an extended period of inactivity or is there another clue?
2. Do you know whether the software update fix for the issue of battery not charging whilst left inactive would have applied to my Nov22 car? How can I tell the update has happened?
3. One AA rep told me a software update takes a lot of load from the 12V battery and could be the cause of it draining (catch22!). Does that sound feasible? What do think about the idea of disabling the internet connection to the car if I'm going to leave it for a while?
4. I might go ahead and go down the power pack route anyway for peace of mind..... and/or trickle charge the battery if I'm leaving it at home.
Thank you

 

[siteguru]

1. If you tap on the 2nd icon from left (at the bottom) in the iSmart app it'll do a scan of the car. One of the scanned items is the 12V battery voltage - if it shows ~13.9V or higher then the 12V battery is being charged up.

3. This is known ... when doing SW updates it is recommended to have an external 12V booster/battery charger connected to the battery.

PS I have a November 22 (registered) SE SR

 

[Tarka]

1. If you tap on the 2nd icon from left (at the bottom) in the iSmart app it'll do a scan of the car. One of the scanned items is the 12V battery voltage - if it shows ~13.9V or higher then the 12V battery is being charged up.

3. This is known ... when doing SW updates it is recommended to have an external 12V booster/battery charger connected to the battery.

PS I have a November 22 (registered) SE SR

Thank you.
So checking the battery voltage whilst I'm away can show me whether it's being maintained.

How do I know when a SW update is due to happen?

 

[siteguru]

How do I know when a SW update is due to happen?

Because the car will be at a service centre, or you'll be attempting your own SW updates. There is no OTA (over the air) update capability with the MG4, so it'll not happen by itself.

 

[Tarka]

Because the car will be at a service centre, or you'll be attempting your own SW updates. There is no OTA (over the air) update capability with the MG4, so it'll not happen by itself.

That's useful. So actually means that's not what's draining the battery whilst I am away. RAC man not quite correct in this case.

 

[Tight Git]

That's useful. So actually means that's not what's draining the battery whilst I am away. RAC man not quite correct in this case.

Also be careful about frequently checking the app whilst on holiday as it wakes the car up and could deplete the 12V battery.

If you can leave the car in a secure garage don't latch the bonnet, so if you need to get to the battery it makes it much easier.