MG4 battery always dead after holiday

[AdamMGEV]

So twice now I've gone on a 2 week holiday. When I return the car is dead. The 12V battery is completely dead.

I make sure I don't open the app and don't have any lights etc on. Surely this isn't right? AA guy says the battery is fine, it's just dead.

 

[Tuareg]

Any modifications to the car, replacement bulbs, added electrical accessories, rerouted cables etc?

 

[webhiker]

So twice now I've gone on a 2 week holiday. When I return the car is dead. The 12v battery is completely dead.

I make sure I don't open the app and don't have any lights etc on. Surely this isn't right? AA guy says the battery is fine.

Doesn't sound right. I have left my Trophy Extended Range for 7 weeks without problems

 

[AdamMGEV]

Any modifications to the car, replacement bulbs, added electrical accessories, rerouted cables etc?

Zero modifications

Doesn't sound right. I have left my Trophy Extended Range for 7 weeks without problems

Mine is one of yhe first MG4s sold. It's a Trophy. Last time it happened the AA guy said this can be common on EV's but don't know why.

 

[jollyman]

So twice now I've gone on a 2 week holiday. When I return the car is dead. The 12v battery is completely dead.

I make sure I don't open the app and don't have any lights etc on. Surely this isn't right? AA guy says the battery is fine, it's just dead.

You’ve got some drain on the battery somewhere because i had an op on my shoulder a replacement joint so I couldn’t drive for 2 1/2 months ,the car wasn’t used for that long ,when I tried it it started up fine And lt drove normally.you need to visit main dealer

 

[AdamMGEV]

You’ve got some drain on the battery somewhere because i had an op on my shoulder a replacement joint so I couldn’t drive for 2 1/2 months ,the car wasn’t used for that long ,when I tried it it started up fine And lt drove normally.you need to visit main dealer

Think I will have to. I very much they will do anything though. AA guy it's very common with all cars.

For the future would this work?

Deal: Car Jump Starter, FLYLINKTECH 2000A Peak 13200mAh Portable Car Battery Jump Starter Booster (up to 6.0L Gas Or 5.0L Diesel Engine), Jump Starter and Power Bank with LED Flashlight, IP67 https://amzn.eu/d/02JG9wS6

 

[siteguru]

Should do .... ?‍

What state of charge did you leave the car at when you went away? (The HV battery is supposed to top up the 12V battery, unless the SoC is "low"* in which case the 12V will be sacrificed to protect the HV battery).

* Anecdotal evidence is that the tipping point is 50% SoC, which is way too high in my opinion.

 

[AdamMGEV]

Should do .... ?‍

What state of charge did you leave the car at when you went away? (The HV battery is supposed to top up the 12V battery, unless the SoC is "low"* in which case the 12V will be sacrificed to protect the HV battery).

* Anecdotal evidence is that the tipping point is 50% SoC, which is way too high in my opinion.

It was at 64%

 

[Tig170]

You can get a bit of corrosion / poor connection on the 12V battery – admittedly not had it on my MG4 (with lower current draw), but have had it on my previous ICE car – the AA said it was a faulty battery, but the battery supplier-Tayna (it was under warranty), serviced it (cleaned terminals) and checked it out, 4 years later no issues. - I bought a little powerbank / jump starter (~£40 from amazon), not had to use on the MG4, but it will crank a diesel tiguan sport, with zero power in the main battery on the key.

 

[dsimpkins]

Loose battery terminals can also be an issue, and sometimes missed by dealer when preparing the car after delivery for the customer.

 

[Tig170]

Loose battery terminals can also be an issue, and sometimes missed by dealer when preparing the car after delivery for the customer.

Exactly, however I left my MG4 for weeks with no issues (in winter & summer), I tend to find that you can't access the car remotely after 1-2 days with the MG app., as mine goes to sleep, have you (OP) been checking daily whilst away?

 

[Coulomb]

I make sure I don't open the app and

Original poster's original words.

 

[pollenface]

It's only a small battery and the wrong kind of battery for cyclic application, it needs a maintenance charger or solar panel to keep it topped up if unused for a couple of weeks.

Both my cars, EV & ICE have solar panels to charge the 12V battery.

 

[decrep]

I'd stick an amp meter in series with the battery, and see if there's any drain while everything is supposed to be off. If that's 0 then the battery itself may have an internal drain.
I'm not sure the AA guy could check for that, the only way I know is to charge it up, and monitor the disconnected voltage for a few days.
But there is some fancy tech stuff these days, it may be possible to do a quick check somehow.

 

[tsedge]

I suspect you need some software updates to stop the drain.

 

[Corindikev]

The AA guys saying a battery will flatten when left for some time being "Common in ALL cars" has nothing to do with the car just the battery. There will always be a very small drain on the 12V battery whenever a car is left with everything turned off as all the electrical equipment while not operating is still connected and numerous microchips are still energised.

The drain is miniscule however and the battery should last for months not just a few weeks even without being charged from the HV traction battery.

There is either something that is drawing power from the battery or the battery itself has an internal fault causing it to discharge. Normally an internal fault manifests itself as short circuit in a cell. This used to be easy to check with old style batteries but most are now maintenance free so hard to detect.

As someone has already suggested get the 12V battery tested for any discharge when everything is turned off. A battery shop or auto electrician can do this easily. If nothing is detected the battery is faulty & needs replacement.

Why it is not being recharged from the HV traction battery is odd unless there is some software that detects the unusual drain and shuts down the recharging process.

 

[AdamMGEV]

Exactly, however I left my MG4 for weeks with no issues (in winter & summer), I tend to find that you can't access the car remotely after 1-2 days with the MG app., as mine goes to sleep, have you (OP) been checking daily whilst away?

Never opened it once. Last time I went away I did, so this time I made sure I didn't.

I suspect you need some software updates to stop the drain.

I'm on the latest one, got it serviced a couple months back and they did it.

 

[Kithmo]

Anything plugged in to the OBDII port, e.g. black box insurance etc. ?

 

[Deleted member 11291]

Or even a usb memory stick? I remember on another forum for a previous ICE car, that someone had the battery draining through this.
Also a dashcam has been known to drain a battery.

Just some thoughts, I hope it gets resolved soon.

 

[tsedge]

I'm on the latest one, got it serviced a couple months back and they did it.

Not talking about Infotainment version - there's a ton of car module updates that fix various bugs including parasitic drain (or so we presume since people with the updates don't seem to have the issue). No, I don't know the specifics, but I got a lot of module updates by complaining about other problems.