12V battery drained in 48 hours whilst locked

[Joningy]

I totally agree.
But if you don’t do any spade work, then they are in no hurry to resolve the problem unfortunately.
Sad I know .

I guess being a mechanical engineer in R&D for the early part of my life made me inquisitive.

I'm now retired and beyond inquisitive if I get my teeth into something, thanks to all for their support and recommendations, this is a great forum and I still love my S5 to drive.

My immediate concern is that we are leaving the car parked at Gatwick for nearly a month near the end of Jan, my wife is concerned as we arrive back to London after 6pm, it'll be dark.

BUT I'm now well practised at getting into the car using the silly spare key with a dead 12v battery

It actually pays to practice, so long as your car key is with you!

In May of 2025 returning from Corfu to Bournemouth, I'd lost my MG4 key, presumably slipped out of my pocket in the hire car or somewhere else in Corfu.

Wife & I had to get a taxi home, about 40+ miles each way, pick up the spare key and the taxi took just me back to Bournemouth airport £140 up the swanny, big learning curve to put car keys somewhere safe.

 

[Ian Key]

Wife & I had to get a taxi home, about 40+ miles each way, pick up the spare key and the taxi took just me back to Bournemouth airport £140 up the swanny, big learning curve to put car keys somewhere safe.

Or you have one key and your wife has the other. You'd be very unlucky to lose both.

 

[Joningy]

Yes that's a possible solution Ian

 

[T1 Terry]

Or you have one key and your wife has the other. You'd be very unlucky to lose both.

The wife and the key?

T1 Terry

 

[Lovemyev]

BUT I'm now well practised at getting into the car using the silly spare key with a dead 12v

I can fully understand that the small emergency blade can be a bit fiddly to use.
Anybody with conditions like arthritis etc would find it hard work especially at night time.
In a situation like this, I wonder if you could get a full sized spare key cut from the pattern on the small blade ?.
I can’t see why not myself .
Although it’s a bit more bulky in size, it would make gaining entry via the drivers door a LOT less challenging .
Just an idea .

 

[Joningy]

I can fully understand that the small emergency blade can be a bit fiddly to use.
Anybody with conditions like arthritis etc would find it hard work especially at night time.
In a situation like this, I wonder if you could get a full sized spare key cut from the pattern on the small blade ?.
I can’t see why not myself .
Although it’s a bit more bulky in size, it would make gaining entry via the drivers door a LOT less challenging .
Just an idea .

@Lovemyev That is a bright idea, I had thought of making something to fit the small key, to enable a better grip and ability to turn the key, but I'll look at your suggestion, firstly I'll see what room is available to turn the key, it only needs a small movement, but of course the door doesn't just pop open, you have to execute a kind reverse Houdini act and pull the handle whist turning the key

 

[Joningy]

My note to Penton MG hand delivered this morning.

"I understood that the main battery is meant to kick in and charge the 12V battery when it drops, even if the car is 'off', is this correct?

if so, what is the minimum HV traction battery SOC to achieve this? I’ve read 20 to 30% or possibly as high as 50% SOC ??? any ideas?

T-Box (Telematics Box) has been found to be at fault on another MGS5.

CCU (Charging Control Unit) is a possibility and causing a possible malfunction of the 12v charging from the main high voltage traction battery!

Results so far. 03/01/2026

I have fully charged the 12v battery using my CTEC MXS-5 smart charger, whilst the negative lead is disconnected to eliminate potential parasitic drawdown.

At the end of the 12v battery charge, I removed the charger, negative battery lead still disconnected, I had a reading of 13.9v, which appears to be spot on.

Fully charged, a further measurement 1.5 hours after removing the charger, to allow the battery to “rest” a reading of 12.98 volts was noted.

12 hours later, in the morning, I re-measured now reading 12.85 volts, this so far indicates a healthy battery.

I will continue to monitor, but if the parasitic drain continues to flatten the battery, it will need MG intervention."

 

[LenEV2016]

My note to Penton MG hand delivered this morning.

"I understood that the main battery is meant to kick in and charge the 12V battery when it drops, even if the car is 'off', is this correct?

if so, what is the minimum HV traction battery SOC to achieve this? I’ve read 20 to 30% or possibly as high as 50% SOC ??? any ideas?

T-Box (Telematics Box) has been found to be at fault on another MGS5.

CCU (Charging Control Unit) is a possibility and causing a possible malfunction of the 12v charging from the main high voltage traction battery!

Results so far. 03/01/2026

I have fully charged the 12v battery using my CTEC MXS-5 smart charger, whilst the negative lead is disconnected to eliminate potential parasitic drawdown.

At the end of the 12v battery charge, I removed the charger, negative battery lead still disconnected, I had a reading of 13.9v, which appears to be spot on.

Fully charged, a further measurement 1.5 hours after removing the charger, to allow the battery to “rest” a reading of 12.98 volts was noted.

12 hours later, in the morning, I re-measured now reading 12.85 volts, this so far indicates a healthy battery.

I will continue to monitor, but if the parasitic drain continues to flatten the battery, it will need MG intervention."

Last paragraph,

please get your finger out and rectify this, as this clear fault is spoiling my otherwise full enjoyment of this car.
Please do not come back to me with there is no fault or this is merely a characteristic as from what I can see on various owners forums is that the only constant MG characteristic is your rather shoddy attitude to aftersales. A fact rather disappointingly backed up in the What Car aftersales and reliability survey.

Many thanks (now get it sorted!)

 

[T1 Terry]

There is a possibility that @Joningy isn't Scottish or of Scottish heritage ..... so he might not be able to produce the full power of the delivery .....

Note, he did post "Hand delivered" Not stuffed down his throat or from the other end until the recipient could taste it to fully understand how strongly he feels about the problem

T1 Terry

 

[LenEV2016]

There is a possibility that @Joningy isn't Scottish or of Scottish heritage ..... so he might not be able to produce the full power of the delivery .....

Note, he did post "Hand delivered" Not stuffed down his throat or from the other end until the recipient could taste it to fully understand how strongly he feels about the problem

T1 Terry

It's all in the rolling of the R's that and the fact that swearing sounds so much better with a Scottish accent (and Irish to be fair)

 

[T1 Terry]

It's all in the rolling of the R's that and the fact that swearing sounds so much better with a Scottish accent (and Irish to be fair)

I don't think rolling my aRse will help in lodging a complaint .... and to tell you the truth, I'm not about to try it to see if it works or not ..... but you are correct, a Scottish accent does instil the fear of further and more serious repercussions .....

On the other hand, an Irish accent over here just brings a smile, hard to take anyone with an accent like that seriously .... you just think it's the first line of a really well presented funny story ..... I just can't picture an Irish person being cranky ....

T1 Terry

 

[Joningy]

There is a possibility that @Joningy isn't Scottish or of Scottish heritage ..... so he might not be able to produce the full power of the delivery .....

Note, he did post "Hand delivered" Not stuffed down his throat or from the other end until the recipient could taste it to fully understand how strongly he feels about the problem

T1 Terry

As a matter of fact @T1 Terry, with the surname of Ingram, although I don't have the accent, there's a strong connection to the Colquhoun clan in the Dunbartonshire region of Scotland, north west of Glasgow.

 

[T1 Terry]

As a matter of fact @T1 Terry, with the surname of Ingram, although I don't have the accent, there's a strong connection to the Colquhoun clan in the Dunbartonshire region of Scotland, north west of Glasgow.

Go get 'em then, I believe that is the next Scottish level about the base level of p*ssed off There could be a higher level, but it's probably in Gaelic and I'm not about to attempt that

T1 Terry

 

[Rolfe]

Don't start me on people who think that where their great-great-granny might have been born gives them some special rights to claim "identity".

 

[LenEV2016]

Don't start me on people who think that where their great-great-granny might have been born gives them some special rights to claim "identity".

Like the whole of USA who don't seem content on just being American.
They need to be Irish American, Italian American, mexican American....... Despite those roots being multiple generations ago

 

[T1 Terry]

The yanks don't have the only claim to that sort of generational claims, it's riff in in Australia as well, mixed with 3rd generation Australian born Slav, Greek, Italian, Lebanese and what ever other flavour you can think of, all identifying as the nationality of their great grand parents, yet couldn't speak the language to save themselves

Just don't understand their thinking, born and raised in the lucky country, but want to identify as something else

My father was born in Kent, son of shop keepers, my mother was born in Australia, youngest of 13 migrated to Australia from Shefield I think .... grandfather was a blast furnace engineer and head hunted to Lithgow Small arms works, then head hunted by the Hoskins Family to build the Port Kembla Steel works ..... I'm proud to call myself an Aussie

T1 Terry

 

[MG Clive]

Like the whole of USA who don't seem content on just being American.
They need to be Irish American, Italian American, mexican American....... Despite those roots being multiple generations ago

Luckily, I don't know any Americans.

 

[Rolfe]

Like the whole of USA who don't seem content on just being American.
They need to be Irish American, Italian American, mexican American....... Despite those roots being multiple generations ago

I remember a German friend saying she met an American who said, on hearing her nationality, "I'm German too!" Whereabouts in Germany are you from, asked Sabine politely. There followed a spiel about the ancestors coming from somewhere in Germany and settling in Iowa in the 19th century.

"That makes you American," replied Sabine.

I did a DNA test just to see if I had anything exotic. They found 2% viking and 2% south-west Ireland, hardly surprising as my father is from the islands, but basically boring as hell. But the fact is, it's not your genetics but your upbringing that defines you.

 

[LenEV2016]

Luckily, I don't know any Americans.

I Once met an American who on finding out I was Scottish proceeded to tell me
His great great great great grandad's brother's wife's aunt's next door neighbour's dog walker's relatives come from Edinboro!!

 

[Joningy]

The yanks don't have the only claim to that sort of generational claims, it's riff in in Australia as well, mixed with 3rd generation Australian born Slav, Greek, Italian, Lebanese and what ever other flavour you can think of, all identifying as the nationality of their great grand parents, yet couldn't speak the language to save themselves

Just don't understand their thinking, born and raised in the lucky country, but want to identify as something else

My father was born in Kent, son of shop keepers, my mother was born in Australia, youngest of 13 migrated to Australia from Shefield I think .... grandfather was a blast furnace engineer and head hunted to Lithgow Small arms works, then head hunted by the Hoskins Family to build the Port Kembla Steel works ..... I'm proud to call myself an Aussie

T1 Terry

Good on-ya fella, interesting background mate, any convicts or Vandemonians in the family Terry?


I totally agree with all you say about new arrivals to our country Terry and not speaking the language, we have loads here, they normally work as delivery van drivers and throw our parcels into a neighbour's garden or just sell the whole f***** van load on a well known auction site.