Twelve Volt Battery Dead after 2 Week Holiday

[cottii2306]

12V battery dead this Monday morning, last used the car on Saturday lunchtime, so fully charged up overnight Sunday. Didn't disconnect charging lead yesterday. Managed to jump start via my wife's car. Lot's of drive assist error messages not working ie picture of a cup of coffee when took for a quick spin.

Interestingly when this happened the previous time the radio stopped working a couple of weeks beforehand, which it did so again this time as well. Radio now working. There must be an electrical fault which slowly discharges the 12V battery when car is in sleep mode ie no key inside and locked.

 

[Jomarkh]

If the radio is having issues then it can drain the 12V battery. Get it looked at under warranty.

 

[WigglePig]

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

WHat voltage does the vehicle usually give for the 12 V battery on the info display?

 

[siteguru]

When driving (i.e. in READY state) mine shows anything from 13.9V to 14.2V. In the iSmart app with the car off and locked I've seen the voltage down to 12.1V

 

[WigglePig]

When driving (i.e. in READY state) mine shows anything from 13.9V to 14.2V. In the iSmart app with the car off and locked I've seen the voltage down to 12.1V

Yup, the battery isn't reaching full charge is what I would suspect. My PFL 5 usually shows 13.8 V which is fine as a float charge voltage but no good for reaching full charge which is going to need 14.4+ V

 

[Ian Key]

My car has been sitting on the driveway since mid-day yesterday and 18 hours later the iSmart app is showing 14.7V and that is after refreshing the screen so it's not showing historic data.

 

[Tuareg]

Something wrong there, resting voltage should be 12.5-12.7V. Running voltage should be 14.3-14.8V. Try refreshing iSmart again.

 

[WigglePig]

My car has been sitting on the driveway since mid-day yesterday and 18 hours later the iSmart app is showing 14.7V and that is after refreshing the screen so it's not showing historic data.
View attachment 34318

14.7 V suggests charging a lead acid battery but the resting terminal voltage should be somewhere around 12.6 V, with float charging around 13.8 V.

I'm still pretty convinced there's something not right with the way that MG EVs treat their 12 V battery or at least how it reports.

 

[Martinonline]

I usually refresh at least twice to get an accurate reading. This morning the first status showed 12.5v but subsequent refreshes showed 12.2v.

 

[DixieTGS]

Agree on the refreshes. It feels like when you ask the app for status it turns on a few circuits in the car and it takes 30s or so for the battery to droop with the extra load.

Mine always used to settle at 3.3 to 3.7V after a few refreshes, depending on when the last 12V top up occurred I assume. Recently it's been 12.1 to 12.5, maybe due to winter or perhaps the battery will need replacing soon . At a recent service they checked it properly and said it was fine so I'm hoping it'll last the summer at least.

 

[Ian Key]

Something wrong there, resting voltage should be 12.5-12.7V. Running voltage should be 14.3-14.8V. Try refreshing iSmart again.

Nothing wrong. The traction battery is charging the 12v battery. I've seen it as high as 14.9v before now.

 

[Tuareg]

You should only be seeing 14V+ when the car is 'Ready' or being driven.

 

[Martinonline]

Agree on the refreshes. It feels like when you ask the app for status it turns on a few circuits in the car and it takes 30s or so for the battery to droop with the extra load.

Mine always used to settle at 3.3 to 3.7V after a few refreshes, depending on when the last 12V top up occurred I assume. Recently it's been 12.1 to 12.5, maybe due to winter or perhaps the battery will need replacing soon . At a recent service they checked it properly and said it was fine so I'm hoping it'll last the summer at least.

13.3 to 13.7v I assume. I've never seen the battery voltage that high when the car is switched off, not charging and locked.

 

[ReintjeWA]

You should only be seeing 14V+ when the car is 'Ready' or being driven.

I think as long as the HV battery is above 50% it will top up the 12v when it needs to, so wonder if it’s possible they just happened to see that happen? Hard to tell though I guess

 

[DixieTGS]

13.3 to 13.7v I assume. I've never seen the battery voltage that high when the car is switched off, not charging and locked.

Aghhh, no idea how i did that. Should have been 12.3 to 12.7 . So the range has just dropped by .2 in the last few months.

 

[nerfmg]

I've had this issue since day 1. If I leave the car for a week then battery will be dead. I've a usb power back 12v booster in the car as an emergency backup.

It's a fun side quest after a holiday. I like the idea of replacing the current 12v with a leisure battery

 

[WigglePig]

Hmm. Since I got involved in this discussion my 5 has started showing 14.0 V when the vehicle is running…

 

[Tig170]

Not sure this is of use or not - SE model from Sept 22, have left the car for over 2 weeks a number of time with no issue.

See attached, the car seems to ping the network every hour, after activity / use. In my case in 24hrs, the battery drops around 0.3v with no use. What I think happens (I've noted this when away, in that I cant communicate with the car after a number of days) is that after a certain amount of time, or battery voltage? the car goes into a deep sleep to preserve the 12V battery.

 

[DixieTGS]

See attached, the car seems to ping the network every hour, after activity / use. In my case in 24hrs, the battery drops around 0.3v with no use. What I think happens (I've noted this when away, in that I cant communicate with the car after a number of days) is that after a certain amount of time, or battery voltage? the car goes into a deep sleep to preserve the 12v battery.

Have you ever seen evidence of the 12V being charged while the car is idle, either via these readings or otherwise?

I'm wondering if the threshold for the car sleeping and the threshold for recharging the 12V is too close together. This would mean on some cars or some occasions, it recharges before going to sleep and so all is good, but other times it goes to sleep and then a bit later recharges, but never comes out of sleep mode until something else happens such as starting the car .

 

[Tig170]

Have you ever seen evidence of the 12V being charged while the car is idle, either via these readings or otherwise?

I'm wondering if the threshold for the car sleeping and the threshold for recharging the 12V is too close together. This would mean on some cars or some occasions, it recharges before going to sleep and so all is good, but other times it goes to sleep and then a bit later recharges, but never comes out of sleep mode until something else happens such as starting the car .

.... only a few evenings into home assistant!, and going in a slightly different direction (with Intelligent Octopus Go) - once I have more data from the MG4 - I'll feedback