Twelve Volt Battery Dead after 2 Week Holiday

[cottii2306]

I purchased my ex-demo MG4 Trophy back in May, 5 months of stress free motoring. On returning from a 2 week holiday last weekend, car parked on my drive plugged in, only to discover the car was completely dead! Luckily, I've RAC cover, they tested the twelve volt battery, it was completely drained on any power. The RAC jumped started the car, I drove it to my local MG4 garage.

The garage workshop tested the twelve volt battery, all ok - and told me (I'm struggling to believe) apparently it isn't unusual for the twelve volt battery to be drained of power if left unattended for 2 weeks! The engineer recommended that someone jumps into the vehicle with the key to start it up if not driven for a couple of weeks! Which at home my daughter can do, however if parked up in an airport car park doesn't work!

Has anyone else experienced a similar issue and been told the same unlikely story / reason. It does seem rather far fetched!

Many thanks

Iain

 

[Martinonline]

The problem has been reported a number of times. Others have left their cars for longer with no problems. The HV battery should keep the 12V battery topped up without the car being powered up but this only happens with the HV battery above a certain state of charge (SOC). What was yours when you left the car?

The problem may not happen again but I, like a number of people here, have a battery booster in case of a low battery. Mine fits in the centre console storage along with a small hammer.

You can search for 12V battery problems for more information. I have not suffered the problem but once I had a low battery voltage warning a year ago which went away after the car was started and has not returned.

 

[cottii2306]

Many thanks Martin for the prompt response. After posting I've read the other similar experiences and the recommendation to purchase a battery booster.

The car was fully charged when we left to go on hols on the 21/9, we returned on the 5/10.

Which battery booster would you recommend?

Thanks

iain

 

[webhiker]

I've left my car for 7 weeks with out any issues, 12V or HV.

PS. I do not recall having read in the manual that HV tops up 12V when not started.

 

[siteguru]

Re. your RAC cover ... all new MGs come with MG Assist - basically AA cover including relay plus and home start. And it renews every following year when you get the car serviced at an MG dealer.

 

[Jomarkh]

Many thanks Martin for the prompt response. After posting I've read the other similar experiences and the recommendation to purchase a battery booster.

The car was fully charged when we left to go on hols on the 21/9, we returned on the 5/10.

Which battery booster would you recommend?

Thanks

iain

Hi, it is better not to leave a car fully charged for days on ends. Keep it at about 80%. Did you say you left it plugged in and if so was that on the 2.2kW granny EVSE?

 

[Dodgy]

Our MG4 was delivered faulty with a parasitic power loss requiring regular jump starts. After the fault was fixed under warranty I replaced the OEM 12V battery with a deep cycle AGM battery (leisure batteries in the UK). AGM batteries have a much slower rate of self-discharge than basic flooded lead acid batteries and this better suits our needs as we’re often away caravanning for extended periods.

The OEM 45 amp hour battery is in the LN1 size/format & I was able to get a 50 amp hour AGM battery in that format which enabled a simple swap. We were recently away 8 weeks and the car started normally on arrival home.

Electric car range test guru Bjorn Nyland reported that some folks in Thailand kept their 12V batteries topped up during periods of non-use by using iSmart to remotely turn on the air conditioning for 10 mins. Use of the air con activates the HV battery which in turn charges the 12V battery. Only potential downside I can see with that option is that seem to get auto logged out of iSmart after a few days.
YouTube link ...

 

[bedsev]

Only potential downside I can see with that option is that seem to get auto logged out of iSmart after a few days.
YouTube link ...

I'm not sure it's logged out, but the car seems to go into a deep sleep and is unresponsibe to the app after a few days locked. I thought this was because my 12V was dead when I left my car for a week, but when I got back to it it was fine after unlocking.

 

[mj224]

I, too, have left the car several times, for a few weeks, and had no problem with the car starting again. About 7 weeks was the longest absence.

However, the 12v battery did fail on me a few months ago. The car was about 3.5 years old at the time..

And a fortune to replace it by the dealer...

 

[Martinonline]

@webhiker, see below.



@cottii2306, below for images of my booster and storage. Note I have not needed to use it so cannot comment on it's effectiveness. Please search for the booster name in this forum and you'll see more information.

 

[siteguru]

I'm not sure it's logged out, but the car seems to go into a deep sleep and is unresponsibe to the app after a few days locked. I thought this was because my 12V was dead when I left my car for a week, but when I got back to it it was fine after unlocking.

Being logged out of the app is very obvious ... you get a Token Expired message and have to login again. If you simply get a Remote Instruction Failed (or similar) message then it is as you say - the car has gone to sleep or there's a comms issue with MG's servers.

 

[jon0881]

there was a bug fix for the software not correctly monitoring the 12v battery. I was a victim of this and been fine since.

 

[JonnyG]

.................Which battery booster would you recommend?

They are pretty effective for the cost and size. Comparison test here :-

 

[OzricEV]

I'd just get the cheapest smart one you can find.

Mine is smaller than my phone and has enough power to jump my 2.5di Convoy with no troubles.

 

[dave99]

I suspect the HV wont charge the 12V if the car is plugged in to a charger?

 

[siteguru]

I'm pretty sure mine does ?‍

 

[Burgo]

FWIW we just left ours for 25 days with main battery at 70% and absolutely no problems firing up when we returned.

 

[JonnyG]

May be best to leave the car locked with no charging cables attached with around 70% to 80% charge and hope the Inteliigent Charging works OK. Leaving a charging cable in suggests it may not do any Inteliigent charging according to the manual.

.

 

[Buster72]

I purchased my ex-demo MG4 Trophy back in May, 5 months of stress free motoring. On returning from a 2 week holiday last weekend, car parked on my drive plugged in, only to discover the car was completely dead! Luckily, I've RAC cover, they tested the twelve volt battery, it was completely drained on any power. The RAC jumped started the car, I drove it to my local MG4 garage.

The garage workshop tested the twelve volt battery, all ok - and told me (I'm struggling to believe) apparently it isn't unusual for the twelve volt battery to be drained of power if left unattended for 2 weeks! The engineer recommended that someone jumps into the vehicle with the key to start it up if not driven for a couple of weeks! Which at home my daughter can do, however if parked up in an airport car park doesn't work!

Has anyone else experienced a similar issue and been told the same unlikely story / reason. It does seem rather far fetched!

Many thanks

Iain

We have left the car for 15 days on a number of occasions and have not had any such problems.

 

[DannySB1]

I'm inclined to think it's one off issue.
I've just come back from a 10-day holiday (Car was on around 40% SOC when I left) When I got back the car booted up without any issues.