Dead 12v battery - any help and advice please?

[Spinynorman]

Mine had an odd 12v battery issue a few weeks ago. I trickle charged the 12v battery for 4 hours and there have been no issues since.

Yeah this is what I do with my mk1 ZSEV. I don’t do much in terms of mileage and don’t leaver her charged to 100% unless I’m going on a drive. Can’t rely on the Zappi 2 to charge the 12v so use a maintenance charger (NOCO) to keep the 12v up to standard. I know some of the MK1s had problems with the original 12v SAICO battery but I’ve only had the odd screen warning that the 12v was low. The NOCO can be left on all the time as it maintains charge, so if there’s any drain, it’ll top it up.
The only thing that worries me is the HV battery growing crystals inside the cells and shorting out but need to do more research on this, as I don’t really understand the risks…

 

[Jto]

you many find this interesting and I would think its possibly the same for full EV

• The market for plug-in hybrid electric vehicles (PHEVs) continues to grow rapidly. Globally, there are now 1.76m PHEVs on the road, and this is expected to reach more than 10 million by 2030, rising at a rate of nearly 20% a year1.
  
  
  A PHEV has two batteries - the main lithium-ion battery, and a reduced size 12V battery that starts the car and looks keeps accessories like heating, air conditioning and computerised systems functioning efficiently.
  
  A few years ago, manufacturers embarked on the development of hybrid models, equipped with a disengageable alternator, capable of reducing emissions and sticking as closely as possible to environmental standards.
  
  But what many PHEV drivers may not realise is that, just like with traditional non-hybrid vehicles, the 12V battery on the PHEV will only charge to 80% capacity while you’re driving the car around. To bring it to 100%, you’ll always need to use a battery charger. What’s more, if you use an intelligent battery charger and maintainer to keep your battery in the best health, you can extend the lifespan of the 12V battery by up to three times!
• If your battery becomes extremely discharged (below 11 volts), there’s a real risk that the battery will suffer long term damage, or even need replacing completely. Below 12.4 volts, sulphation can start to build up on the lead elements of the battery, degrading it.
• At between 12.4 and 12.65 volts, the battery still has the power it needs to start the car, but a charge is recommended. You have to act quickly to prevent the battery from degrading quickly and irreversibly.
• A lead acid battery is considered fully charged at 12.72 volts.

 

[m4rmite]

MG5 SR late 2020. Just got back from 5 days away having left car standing on drive as usual.Car was turned off and locked.

Keys (both) wouldn't unlock the car. Appeared completely dead. Unlocked manually and car would not turn on. Opened bonnet and removed cover. Disconnected 12volt battery - it measures 2.5 volts open circuit...

Ok so something has caused the battery to go flat. I have it on charge now which may or may not recover it.

The question is how will it be safe to reconnect it and how much current should be drawn from the 12v with the car off?

What can have caused the battery go flat? Has anyone else experienced this? When I left it last week the state of charge on the HV was about 50% - of course I have no way of telling what it is now, I can't unlock the front flap to plug in the charger (which is what I was going to do as I need it fully charged in the morning.

I'm fingers crossed it will at least wake up when the 12v has had a couple of hours charge - but it is very worryng that simply leaving the car for 5 days it will go dead - we have left it for much longer before so something must have gone wrong. Any ideas what. Anyone else had similar?

Just to add that the car as left unattended for 2.5 weeks late june-early july with no problem. The 12v battery state normally shows 14+ volts - and was doing so last week. Never seen it lower than 13.5v. All seemed normal week ago. Seems unlikely that the battery simply fell off a cliff in 5 days.

I left mine for 8 days at an airport carpark and it was fine.

What I mean is that it must be an exception rather than the rule.

 

[johnb80]

you many find this interesting and I would think its possibly the same for full EV

• The market for plug-in hybrid electric vehicles (PHEVs) continues to grow rapidly. Globally, there are now 1.76m PHEVs on the road, and this is expected to reach more than 10 million by 2030, rising at a rate of nearly 20% a year1.

I can see many EV haters taking the PHEV option ignoring the EV aspect of the car.

A PHEV has two batteries - the main lithium-ion battery, and a reduced size 12V battery that starts the car and looks keeps accessories like heating, air conditioning and computerised systems functioning efficiently.

When you say 'starts' the car, I assume youre meaning supplies all of the ancillaries like radio, instruments, fan, wipers, lights etc rather than starting the engine which it usually does not.

A few years ago, manufacturers embarked on the development of hybrid models, equipped with a disengageable alternator, capable of reducing emissions and sticking as closely as possible to environmental standards.

They certainly had intelligent charging control, I've not heard of any where the alternator can be disengaged. Many Hybrids have various oddities around them, our Outlander PHEV used the big alternator to start the engine, some small hybrids use the engine alternator to start the engine via the aux belt.

But what many PHEV drivers may not realise is that, just like with traditional non-hybrid vehicles, the 12V battery on the PHEV will only charge to 80% capacity while you’re driving the car around. To bring it to 100%, you’ll always need to use a battery charger. What’s more, if you use an intelligent battery charger and maintainer to keep your battery in the best health, you can extend the lifespan of the 12V battery by up to three times!

I'm not convinced this is true, definitely not so for ICE vehicles, nor would I expect it for EV's or Hybrids either. A lead acid battery should never be discharged beyond 50% of it's capacity, if charging stopped that would only give a usable capacity of 30% of the battery rating, thats not going to cut it.

• If your battery becomes extremely discharged (below 11 volts), there’s a real risk that the battery will suffer long term damage, or even need replacing completely. Below 12.4 volts, sulphation can start to build up on the lead elements of the battery, degrading it.

12V sealed lead acid batteries are fully charged at around 12.89 volts and fully discharged at around 12.23 volts (assuming 50% max depth of discharge). 12V flooded lead acid batteries are fully charged at around 12.64 volts and fully discharged at around 12.07 volts (assuming 50% max depth of discharge).

• At between 12.4 and 12.65 volts, the battery still has the power it needs to start the car, but a charge is recommended. You have to act quickly to prevent the battery from degrading quickly and irreversibly.

12.23v is the minimum (50%)

• A lead acid battery is considered fully charged at 12.72 volts.

12.89v, it does vary with temperature though.

 

[staarek]

MG5 SR late 2020. Just got back from 5 days away having left car standing on drive as usual.Car was turned off and locked.

Keys (both) wouldn't unlock the car. Appeared completely dead. Unlocked manually and car would not turn on. Opened bonnet and removed cover. Disconnected 12volt battery - it measures 2.5 volts open circuit...

Ok so something has caused the battery to go flat. I have it on charge now which may or may not recover it.

The question is how will it be safe to reconnect it and how much current should be drawn from the 12v with the car off?

What can have caused the battery go flat? Has anyone else experienced this? When I left it last week the state of charge on the HV was about 50% - of course I have no way of telling what it is now, I can't unlock the front flap to plug in the charger (which is what I was going to do as I need it fully charged in the morning.

I'm fingers crossed it will at least wake up when the 12v has had a couple of hours charge - but it is very worryng that simply leaving the car for 5 days it will go dead - we have left it for much longer before so something must have gone wrong. Any ideas what. Anyone else had similar?

Just to add that the car as left unattended for 2.5 weeks late june-early july with no problem. The 12v battery state normally shows 14+ volts - and was doing so last week. Never seen it lower than 13.5v. All seemed normal week ago. Seems unlikely that the battery simply fell off a cliff in 5 days.

Had a similar issue recently, left the car at airport parking for 2 days and the battery was dead on our arrival, had to call AA etc. The issue solved itself since, i suspect that 12v battery got discharged as infotainment wasn't switching off fully. Prior to the issue we had "radio module initialising" displayed and i think this might have prevented from switching audio system when the car was off. The radio is all good now, and the 12v battery is also at 12.5v-12.6v when switching the car in the morning.

 

[Rayz]

I've just had the same problem. After leaving my car parked for 5 days whilst visiting friends in Germany. I found my 12v battery was flat. I used the key in my key fob, a 10mm spanner and a new battery and the job was finished in ten minutes. The old Chinese 12v battery would not hold a charge. It was 2 years old.

What type of EV car did you put it on, and what type of battery was put on please. Thanks

 

[Mundiz]

I have an MG ZS EV Exclusive 2021 and I replaced the old Chinese battery with a 12v Caravan Battery. Just get one the same dimensions as the old battery.

 

[Sinc]

Have a 10 week old ZS LR Trophy. Week 7ish, after not using 2 days & with 73% SoC, encountered same problem. Not technical so called MG Assist, AA there within 20 mins, 12v battery checked, showed 3v. Battery given enough charge to allow systems to engage, SoC showed 73%. Hours drive and, touch wood no further problems. However just as worrying though, in my area(south coast), to get it checked under warranty by nearest MG dealer (5miles), quoted 10 weeks although managed to get slot from another dealer(20 miles) for 6 weeks! Will post results when known.

 

[Jto]

Have a 10 week old ZS LR Trophy. Week 7ish, after not using 2 days & with 73% SoC, encountered same problem. Not technical so called MG Assist, AA there within 20 mins, 12v battery checked, showed 3v. Battery given enough charge to allow systems to engage, SoC showed 73%. Hours drive and, touch wood no further problems. However just as worrying though, in my area(south coast), to get it checked under warranty by nearest MG dealer (5miles), quoted 10 weeks although managed to get slot from another dealer(20 miles) for 6 weeks! Will post results when known.

I would give the 12v battery a charge with a 12v battery charger, do you do short journeys or only use every other day? You can go to Halfords and they check the battery for free, I have asked them But only after a charge and ask for the capacity of the battery not just the voltage.

 

[Sinc]

I would give the 12v battery a charge with a 12v battery charger, do you do short journeys or only use every other day? You can go to Halfords and they check the battery for free, I have asked them But only after a charge and ask for the capacity of the battery not just the voltage.

Nice to know Halfords will do a check for free. Journeys no different than with ICE car, and lets be honest, shouldn't have a battery problem with a two month old vehicle. So MG dealer can sort but thanks anyways.

 

[Jto]

No it should not but standing and short journey the battery may not recover its capacity which is different to voltage, most of the 12v battery problems resulting from under use or short journeys where the battery has not had sufficient time to recover to full capacity or after speaking with my dealer is minicab drivers who between jobs have the radio on as the car is only in ready mode (driving ) for short time.

 

[Mundiz]

My 12v battery failed but that was after 2 years. I was told that the quality of Chinese batteries fitted to MGs is poor, especially when not drip charged every day by driving every day.

 

[Deep purple]

Went away for 2 weeks (without car) and when I got back decided to see what the state of the 12v battery was. So pressed start/stop button twice without foot on brake. The 12 volt battery showed 11.8 volts and dropping which suggested that it was at a low state of charge. Took car for a 20 minute drive, during which obviously the 12v battery was being charged and on return did the same trial again. Battery voltage 12.2 and steady so the battery had clearly been recharged a bit.
This leads me to 2 possible conclusions, either the 12 volt battery is in a bad way and so self discharging, or there is something in the car which is using 12 volts when the car is fully shutdown. I have no gadgets or gizmos so if there is a load it is probably the car reporting back to China.
Car is pre FL LR and 18 months old.
All my previous cars over the last 15-20 years have had batteries which lasted 8-10 years.

 

[Jonhklee]

Went away for 2 weeks (without car) and when I got back decided to see what the state of the 12v battery was. So pressed start/stop button twice without foot on brake. The 12 volt battery showed 11.8 volts and dropping which suggested that it was at a low state of charge. Took car for a 20 minute drive, during which obviously the 12v battery was being charged and on return did the same trial again. Battery voltage 12.2 and steady so the battery had clearly been recharged a bit.
This leads me to 2 possible conclusions, either the 12 volt battery is in a bad way and so self discharging, or there is something in the car which is using 12 volts when the car is fully shutdown. I have no gadgets or gizmos so if there is a load it is probably the car reporting back to China.
Car is pre FL LR and 18 months old.
All my previous cars over the last 15-20 years have had batteries which lasted 8-10 years.

Same here. New battery fitted, still self discharging overnight. I now trickle charge the 12V in my garage when I don’t drive it. I get random Parking system faults when the 12v discharges itself! Going to ask MG to sort it. New battery didn’t sort it in the end, but my 2.5 years old Pre-FL, so expecting the original 12V needing replaced anyway. Car seems to need the 12V in full state of charge constantly!