12v battery losing charge

[EssBees]

Hi, apologies if I'm posting in the wrong area, it's my 1st time on here. I'm hoping for some advice wrt my 12v battery.
I have a 12 month old ZS SE long range. Monday night I charged to 100% as I was making a 250 mile round trip on Tuesday. On my return home I was running low so started charging to 80%. When I went to disconnect from the charger to take the car out this afternoon the car was completely dead. (I needed to use the little key in the fob to gain entry and release the emergency pull to undo the charging cable). The AA came out and found main battery fully charged to 80% as planned but 12v at 1.75v. Nothing had been left on overnight. When the charging cable was connected we could see the 12v battery taking a charge (much higher rate than charging just with car powered up). When the main battery was not charging ie set the limit to below 80% and no charge was going into the car, the 12v battery had 7 amps coming out. If I disconnected the cable, then the charge lost from the 12v battery whittled down to almost 0.
It seems if I am able to disconnect soon after achieving a full charge I should be OK ( I have my fingers crossed it will get me to work tomorrow morning) but something isn't right. Will this most likely be an issue with the car for MG to look at, my charging cable or my charger? The car is booked in for it's first year service in a couple of weeks but is this something I should raise before? Anyone had anything similar and how was it sorted? Thanks for any info.

 

[TassieDi]

Sounds like a problem with the 12V battery. See if you can bring the dealer visit forward.

 

[EssBees]

Sounds like a problem with the 12V battery. See if you can bring the dealer visit forward.

Thanks. I have now spoken to the call centre for my charger and was told that they would expect the amp drain if I leave the car connected after a charge (!?) and to avoid it I should schedule the charge to finish at a time I'm ready to disconnect. I appreciate this would solve the problem I'm just surprised as the charger I installed at my previous home (I've recently moved) I could leave connected as long as I wanted with no drain to my 12v battery. Hey ho, think I may look to change my charger back to what I'm used to.

 

[Lovemyev]

Thanks. I have now spoken to the call centre for my charger and was told that they would expect the amp drain if I leave the car connected after a charge (!?) and to avoid it I should schedule the charge to finish at a time I'm ready to disconnect. I appreciate this would solve the problem I'm just surprised as the charger I installed at my previous home (I've recently moved) I could leave connected as long as I wanted with no drain to my 12v battery. Hey ho, think I may look to change my charger back to what I'm used to.

Just a thought have you tried using the Granny lead and see if it follows the same pattern ?.
If the 12 volt battery does not discharge while the Granny is still plugged in, then it’s your wall box that causing the issue surely ?.
If the 12 volt battery still continues to discharge when using the Granny, then it is likely to be a bad 12 volt battery or the car has a parasitic drain.

 

[EssBees]

Just a thought have you tried using the Granny lead and see if it follows the same pattern ?.
If the 12 volt battery does not discharge while the Granny is still plugged in, then it’s your wall box that causing the issue surely ?.
If the 12 volt battery still continues to discharge when using the Granny, then it is likely to be a bad 12 volt battery or the car has a parasitic drain.

That's a good call, thanks. Hadn't thought to try that. I will give it a go.

 

[Lovemyev]

That's a good call, thanks. Hadn't thought to try that. I will give it a go.

You are very welcome !.
Even if your preference is the use of a wall box, then having a Granny lead is a good back up / proving unit to detect wall box issues.
A relative of mine had recently upgraded from the Gen1 ZS EV to the Gen2 LR.
A couple of days after bringing his car home, he found that his smart Rolec wall box was failing to commence a charge.
He called in a flap saying it had to be the car, because it was fine on his old car.
On was at the weekend and both the service department at the dealer was closed and the firm that installed his wall box.
He had a hospital appointment on the Monday and was in a blind panic .
He had completely forgotten about the Granny unit stored in the boot.
Five minutes later and he was charging again.
It turned out to be a faulty type 2 charging lead and not the car at all.
One lesson learnt when owning an EV is always, try and have a fall back plan if you can.
Is it worth maybe considering installing a battery monitoring device in the future ?.
Easy to install and it runs through an App on your phone.
If the SOC level of the 12 volt battery drops too low, it will notify you via your phone.
I have included a link for your consideration.

Car Battery Monitor BM2,12V Car Battery Monitor Tester BM2 Device Leisure Battery Tester, for Android IOS Phone BM2 Bluetooth 4.0 and Above
https://amzn.eu/d/4NBicKH

 

[Coulomb]

Also check to see that the 12 V battery voltage increases when you go to ready. If not, it is the DC-DC, not the 12 V battery.

BTW, the battery that ended up at 1.75 V will almost certainly be ruined.

 

[Lovemyev]

BTW, the battery that ended up at 1.75 V will almost certainly be ruined.

Agreed !.
When a 12 volt battery depletes to a SOC this low, is difficult to be confident in its ability to hold a decent charge anymore even after a slow recon charge.

 

[TassieDi]

My service centre confirmed to me that Intelligent Charging should ensure that the 12V battery remains fully charged. i.e. the "transport" battery will top up the "house" battery, as required. There should be no need to specifically turn off HVAC etc when leaving the car. It should not be necessary to operate the car more often than every couple of months to ensure all systems remain in best condition.

 

[Lovemyev]

This very true, but remember if you run 12 volt items when the car is only in STANDBY mode and not in the fully READY mode, you will flatten the 12 volt battery !.

 

[ZSchat]

I have to say that the reports of low 12v battery issues have worried me so I hope that we can trust what your service centre says about intelligent charging keeping it topped up. I find the manual less re-assuring. To quote:
"The 12v battery SOC is constantly monitored, when the Start/Stop switch is in the OFF position it is possible, under certain conditions, that the HV battery will automatically charge the 12v battery to ensure the vehicle starts".
Only 'possible' and 'under certain conditions' then - hardly definitive! Further, it appears that intelligent charging will be suspended if the HV battery SOC is low, which makes sense but it doesn't say how low.

 

[N2STY]

The 12v battery only charges in ready mode or when HV battery is charging or when HV battery is in use ie when running AC with the app it doesn't charge when car is off or in auxiliary mode

 

[ZSchat]

So not really intelligent charging and completely at odds with what the manual says then

 

[Peter WA]

I too can't find the "intelligent charging" happening.

If it works for anyone, it would be great to know at which 12V battery voltage it kicks in, what the minimum SOC of the HV battery is for it to work, and how often the voltage is checked.

I'm just back from a 3 week absence, and was very glad that I had someone to plug in the car to charge, because the 12V battery was on a trajectory that would have left it dead otherwise. Here's a chart:

I last charged the car on June 12th, before leaving. From then on the 12V battery slowly lost charge, until I decided to ask someone to plug the car into the charger for me on June 27th.

The 11.7V it dropped to on June 27th correspond to 20-30% remaining charge. Way too low, it should never have gone there.

Since there's no detailed information available from MG and they are impossible to contact don't reply to any questions, I decided to buy a good quality 12V battery charger, and will hook it up whenever I go away for more than 1 week.

Cheers,

Peter

P.s.: I do realise that having OVMS connected will ever so slowly drain the 12V battery. It might have contributed as much as half of the observed volt drop. Still, even without OVMS, the battery would have approached "dead" after 4 weeks in any case, instead of the 2 weeks I observed.

 

[ZSchat]

If I'm reading what N2STY says correctly then the 12v battery is never going to charge if the car is off. However I am convinced mine was at 12.9% when I left the car a couple of days ago and it registered 14.5v when I started it yesterday so I'm with you - I would really, really like a definitive answer. Of course it could just be that the iSmart app; is not that reliable in reading/sending 12v battery SOC.

 

[N2STY]

It will always read higher once switched on as the DC to DC activates you can switch on with out brake pedal depressed then look at voltage that will give you a better reading
The 12v battery will charge when car is off if it charging the HV battery or if you activate certain equipment with the app for 10 mins

 

[ZSchat]

Thanks for clarification. It seems that the "intelligence" doesn't help to ensure the car will start (which would be really handy) per the claim in the manual so a bit disappointing really. Getting a bit nervous of leaving the car for any length of time now

 

[Tim Green]

Ref Essbess, surely if you have a 7A drain from the 12v battery through your charging cable there must be something wrong with your charger?

 

[ZSchat]

So I suppose what I really want to know is whether the car will be dead if I go away and leave it for 2 weeks?

 

[N2STY]

So I suppose what I really want to know is whether the car will be dead if I go away and leave it for 2 weeks?

Left mine at airport 14 nights it was fine I had booster pack if needed anyway but there is always the free mg\aa cover