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MG Electric Vehicle Enthusiasts
MGS5 12V battery dead
- Thread starter Shwd mae
- Start date
emmrecs
Established Member
@dx4100
Thanks again, and understood, again!
Unfortunately, although my wife has an ICE car there's no room to park it in front of mine without also blocking access for my neighbours; we have a shared main drive, with my section of it just long enough to park the S5 in front of my garage door. And, inevitably, the garage is used for storage of everything except a car!
My car is booked into my local dealer for a full day's diagnostics, though not until next Thursday, December 18th.
And, so as to be "safe rather than sorry" I've just topped up the booster pack so it's primed and ready for when/if it's needed again!
I'm fairly sure the problem is some parasitic drain; having had the AA restart the car on Monday my wife and I took a journey of some 50 miles and the car stayed "active" right through the next day, without being driven and only this morning did it decide to not play ball.
EDIT: to add, I think the critical phrase in that section of the manual which you quote is
The system will suspend intelligent charging if a fault is present. Presumably whatever is causing the problem is viewed as a "fault"?
Thanks again, and understood, again!
Unfortunately, although my wife has an ICE car there's no room to park it in front of mine without also blocking access for my neighbours; we have a shared main drive, with my section of it just long enough to park the S5 in front of my garage door. And, inevitably, the garage is used for storage of everything except a car!
My car is booked into my local dealer for a full day's diagnostics, though not until next Thursday, December 18th.
And, so as to be "safe rather than sorry" I've just topped up the booster pack so it's primed and ready for when/if it's needed again!
I'm fairly sure the problem is some parasitic drain; having had the AA restart the car on Monday my wife and I took a journey of some 50 miles and the car stayed "active" right through the next day, without being driven and only this morning did it decide to not play ball.
EDIT: to add, I think the critical phrase in that section of the manual which you quote is
The system will suspend intelligent charging if a fault is present. Presumably whatever is causing the problem is viewed as a "fault"?
dx4100
Standard Member
Its a bit cryptic and intentionally vague it feels. It says it works "under certain conditions" without suggesting what those conditions maybe. I get a feeling those conditions are in addiitonal to the "The system will suspend intelligent charging if a fault is present".
Starting and suspending are not the same thing.
See what the dealer says and if you don't mind could you provide an update here. I will test my battery tonight and let you know what condition it is in. So if it dies I can confirm it did so from a healthy state at least.
Defo do as much as you can though to get that thing charged up. Maybe take a couple of extra trips.
Starting and suspending are not the same thing.
See what the dealer says and if you don't mind could you provide an update here. I will test my battery tonight and let you know what condition it is in. So if it dies I can confirm it did so from a healthy state at least.
Defo do as much as you can though to get that thing charged up. Maybe take a couple of extra trips.
Lovemyev
Distinguished Member
While on the subject on charging the 12 volt battery.
I have noticed that there is a difference between the S5 and both of our two previous ZS EV’s.
Also as soon as the ZS EV is in READY mode, the battery voltage is displayed about at 14.1 volts.
This is very close to what you would expect to see from a ICE car that is equipped with an alternator, to replenish the battery condition.
The charge rate is normally about 14 to 14.2 volts.
I have noticed that the S5 is different in our car at least
.
When the car is first placed into READY mode, then swipe the head unit screen, to reveal the battery status, it is normally displaying around 13.5 volts and not 14.0 volts.
Yeah - 13.5 volts is okay, but as a journey progresses, the battery status increases much more slowly, reaching 13.8/9 volts, then hitting the 14 volts after some time ?.
Does this difference suggest anything I wonder.
Is the actual battery
size / storage capacity a little on the small size ?.
Is the 12 volt battery charging software profile on the S5 just a little more lethargic than the ZS EV model ?.
Therefore taking longer to replenish the battery ?.
If so, then this may explain why taking a lot of small trips, it slowly diminishes to a point when the status is too low to bring the car into READY mode ?.
Failing this the battery itself is failing to retain the energy, or there has to be some type of constant parasitic drain problem.
These are just my own personal observations of course.
I have noticed that there is a difference between the S5 and both of our two previous ZS EV’s.
Also as soon as the ZS EV is in READY mode, the battery voltage is displayed about at 14.1 volts.
This is very close to what you would expect to see from a ICE car that is equipped with an alternator, to replenish the battery condition.
The charge rate is normally about 14 to 14.2 volts.
I have noticed that the S5 is different in our car at least
.When the car is first placed into READY mode, then swipe the head unit screen, to reveal the battery status, it is normally displaying around 13.5 volts and not 14.0 volts.
Yeah - 13.5 volts is okay, but as a journey progresses, the battery status increases much more slowly, reaching 13.8/9 volts, then hitting the 14 volts after some time ?.
Does this difference suggest anything I wonder
.Is the actual battery
size / storage capacity a little on the small size ?.Is the 12 volt battery charging software profile on the S5 just a little more lethargic than the ZS EV model ?.
Therefore taking longer to replenish the battery ?.
If so, then this may explain why taking a lot of small trips, it slowly diminishes to a point when the status is too low to bring the car into READY mode ?.
Failing this the battery itself is failing to retain the energy, or there has to be some type of constant parasitic drain problem.
These are just my own personal observations of course.
dx4100
Standard Member
So the car has been doing its usual small journeys since the failure on Sunday and is going to do its "big" trip to Leeds in the morning. I thought I would get a battery reading before and it doesn't look great.
SOH = 100% - as you would expect for a new car
SOC = 70% - so its 28% down from Sunday but you should be good down to around 20%
Volts = 12.42 - this is about what you should see from a 70% charged battery. And an EV probably needs something like 11.5 to 12.5 to start up so we are good here.
The car is currently on charge ready for the trip in the morning. If I have time I will take another reading to see if charging the main battery does anything to top up the 12V.
I will also take another reading when I get back from Leeds to see how it looks.
We also have no plans to use the car Friday evening to Sunday afternoon so it will be interesting to see how it does without a couple of days use. Will take readings.
Something I have noticed though is my battery tester isn't as reliable testing this battery like normal car batteries. I think the battery is a bit of heap of junk to be honest.
Oh and in other developments. I get my car on lease through Tuskers (work salary sacrifice scheme). I chatted to them about the issue with the battery at the weekend and they want it booking in with the dealer for a once over. So its going in for a check up at some point when Tuskers arrange it.
SOH = 100% - as you would expect for a new car
SOC = 70% - so its 28% down from Sunday but you should be good down to around 20%
Volts = 12.42 - this is about what you should see from a 70% charged battery. And an EV probably needs something like 11.5 to 12.5 to start up so we are good here.
The car is currently on charge ready for the trip in the morning. If I have time I will take another reading to see if charging the main battery does anything to top up the 12V.
I will also take another reading when I get back from Leeds to see how it looks.
We also have no plans to use the car Friday evening to Sunday afternoon so it will be interesting to see how it does without a couple of days use. Will take readings.
Something I have noticed though is my battery tester isn't as reliable testing this battery like normal car batteries. I think the battery is a bit of heap of junk to be honest.
Oh and in other developments. I get my car on lease through Tuskers (work salary sacrifice scheme). I chatted to them about the issue with the battery at the weekend and they want it booking in with the dealer for a once over. So its going in for a check up at some point when Tuskers arrange it.
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Lovemyev
Distinguished Member
You can see a “live” read out of the 12 volt battery status, when you are on the move tomorrow, view it in the head unit of the car.
Some EV drivers ( not just MG ) have taken the decision to purchase a battery status monitor, that is easily fitted onto the battery terminals.
It constantly checks the status of the 12 volt battery and will even send a notification to your phone, if the charge status / condition of the 12 battery drops too low.
You can down load the free App and then check on the condition of your 12 volt battery as and when you please.
There are about £20 ( ish ) to buy.
I know a few Kia Nero owners who have found these devices a big help in avoiding the possibility of returning to the car and discovering a completely flat 12 volt battery.
This is a popular type of unit used.
Some EV drivers ( not just MG ) have taken the decision to purchase a battery status monitor, that is easily fitted onto the battery terminals.
It constantly checks the status of the 12 volt battery and will even send a notification to your phone, if the charge status / condition of the 12 battery
drops too low.You can down load the free App and then check on the condition of your 12 volt battery as and when you please.
There are about £20 ( ish ) to buy.
I know a few Kia Nero owners who have found these devices a big help in avoiding the possibility of returning to the car and discovering a completely flat 12 volt battery.
This is a popular type of unit used.
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I may pick one up 
I replaced the one on my MG4 as a precaution after 18 months with a Yuasa YBX5012 from Amazon and I will do the same after the 12 month 12V battery warranty runs out on the MGS5. I haven't checked but I guess the battery on the MGS5 is the same size.
The car seemed to have less fleeting software glitches but that may have been because the battery was disconnected and reconnected rebooting all the software.
The car seemed to have less fleeting software glitches but that may have been because the battery was disconnected and reconnected rebooting all the software.
As an Amazon Associate we earn from qualifying purchases.
dx4100
Standard Member
Lovemyev
Distinguished Member
13.9 volts vs 14.0 volts is as close as does not make any difference tbh.
I am willing to bet, that had you put the car in ready mode first, it would be bang on 15.0 volts.
What did the car report the 12 volt battery voltage as, in the head unit ?.
Checked mine “on route” this morning at the traffic lights, 14.0 volts reported.
They really should add the battery volt to the health report on the App !.
ARE YOU LiSTENING MG
.Wyeknot
Standard Member
Sidetrack back to booster packs if I may, and their storage. Would it be ok to store one under the bonnet - suitably wrapped and secured? Bonnet release would still work if 12v dies, and I'd feel happier with it NOT under a seat in the cabin!
Shwd mae
Standard Member
Perhaps I'm incorrect here, but I think that the fact that the 12V battery shouldn't be draining so quickly in the first place. We shouldn't have to be thinking about fitting battery monitoring systems and carrying jumpstart kits, after spending our hard earned money on a new car.
Surely we should have confidence that if we leave the car unused for a few days, let alone overnight that it will still start.
Unbelievable that an EV has a problem with a 12V battery in the first place.
Surely we should have confidence that if we leave the car unused for a few days, let alone overnight that it will still start.
Unbelievable that an EV has a problem with a 12V battery in the first place.
dx4100
Standard Member
True... but...
I am almost certain it was my fault the battery went flat. I think I actually turned the car off instead of the screen at one point. You can drain the battery in a ICE car as well to be fair.
Some people have had genuine parts failures and I think some of us (me) are just learning the hard way how to use the car.
I am almost certain it was my fault the battery went flat. I think I actually turned the car off instead of the screen at one point. You can drain the battery in a ICE car as well to be fair.
Some people have had genuine parts failures and I think some of us (me) are just learning the hard way how to use the car.
I store mine under the centre armrest between the front seats. I bought a tray that fits on top from AliExpress similar to this one.
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