Brand new 12V battery discharging

[CallMeDave]

Hello,

I have an issue which might be car related, battery related or both.
I bought a 4 year old MG ZS, still under warranty, from Cinch about 5 months ago.
It worked without issue. We use it infrequently (2 or 3 times per month). In November there were issues starting the car. The 12V seemed to be discharged.
I tried to boost start the car with mixed success. The computer would start but the 12V didn't seem to charge and the drive wouldn't engage.
I trickle charged the 12V but it didn't seem to hold a charge.
Given these batteries have a limited life I chalked it up to the battery being old. I bought a new one with the same specs as previous one and listed as compatible with the car "Halfords AGM027 Start Stop Car Battery".
We drove the car twice and it worked both times. Then on Christmas day it would not start despite being fully charged a few days before. Cue 2 very upset young children...
I trickle charged it again and the computer started but continued to throw up every error possible i.e. none of the electronic or smart systems working.
I read online that sometimes the computer goes wrong after the battery is disconnected and reconnected and it might need some time to settle. Sure enough after a few hours when I tried again the car started and we were able to drive it. The next day the battery was discharged again and the car wouldn't start.

To try to separate battery and car issues, I trickle charged the battery and left it completely disconnected. Immediately after charging I got a reading of 11.84V from the battery terminals.
After ~30 hours (completely disconnected and unused) the reading is 10.82V. Is that normal?
The temperature is currently 1°C. I'm not sure if there is a temperature impact and perhaps the battery was warmed by the charging process so what I'm measuring is the difference between a warm and cold battery.

I did a continuity test on all the fuses with exposed terminals. They were fine. (I didn't remove and test the fuses that had a fully plastic top).

So, did I replace a dud battery with a brand new dud battery? Seems improbable.

Car is still within 6 months of purchase (barely) so I need to decide to go back to Cinch or go for manufacturer's warranty or back to Halfords for a replacement battery.

Thanks,
Cameron

 

[Jomarkh]

The car doesn't need much to go into ready mode. You can get hand held boosters that do the job and once in ready mode the HV battery will charge the 12V one. If you don't use the car much then think about getting a trickle charger for the 12V battery.
Are you able to get your home EVSE (charge point) to get the car back to life?

 

[Gadget Geek]

If the battery was only reading 11.84V after charging then you need to get your money back. It should read somewhere around 13-14V after a full charge.

There are a few threads about 12V batteries on the forum. If you use the search function you will find them, and some members give recommendations of replacement batteries.

 

[Coulomb]

To try to separate battery and car issues, I trickle charged the battery and left it completely disconnected. Immediately after charging I got a reading of 11.84V from the battery terminals.

That's a problem right there: the battery is almost completely dischsrged at this point. Hiw long did you trickle charge it? What actual current?

After ~30 hours (completely disconnected and unused) the reading is 10.82V. Is that normal?

Starting at 11.85V and being so cold, it's not great but understandable. Hopefully it didn't lose too much capacity with that treatment. Lead acid batteries don't like staying at low states of charge for long periods.

My guess is that the "new" battery was on the shelf for months, and was at a low state of charge. Really it should have been charged overnight before use. Perhaps it didn't get much use to charge it up.

The other thing is that I've never heard my ZS 2021 EV recharge the 12V battery, even though it's right outside my bedroom window. I've heard the Nissan Leaf do it plenty of times. Granted, the MG contractors seem to be very quiet compared to the Leaf's. But I suspect that at least some early ZSs simply don't recharge the 12V battery. If so, you might have to rig up a quick disconnect for a trickle charger, especially if it will be left unused for some time.

 

[Eclectic]

Immediately after charging you should get a reading of 13.5-14V. Anything after standing below 12.3V and I would be suspecting a faulty battery.

 

[CallMeDave]

That's a problem right there: the battery is almost completely dischsrged at this point. Hiw long did you trickle charge it? What actual current?

I used a Noco Genius 5 (set to 12V AGM). The battery was disconnected from the car while charging.
I charged it for 6 hours which was long enough for the indicator to go completely green plus an extra ~hour.
I didn't measure current but I can try to charge it again and measure.

Starting at 11.85V and being so cold, it's not great but understandable. Hopefully it didn't lose too much capacity with that treatment. Lead acid batteries don't like staying at low states of charge for long periods.

My guess is that the "new" battery was on the shelf for months, and was at a low state of charge. Really it should have been charged overnight before use. Perhaps it didn't get much use to charge it up.

I charged it for 3 hours before using it. I had read conflicting things about charging new batteries so I went for the compromise of partially charging it (charger states 6 hours for a full charge on most batteries).

The other thing is that I've never heard my ZS 2021 EV recharge the 12V battery, even though it's right outside my bedroom window. I've heard the Nissan Leaf do it plenty of times. Granted, the MG contractors seem to be very quiet compared to the Leaf's. But I suspect that at least some early ZSs simply don't recharge the 12V battery. If so, you might have to rig up a quick disconnect for a trickle charger, especially if it will be left unused for some time.

Thanks for the tip. We are likely to use it only a few times per month (about 100 miles per round trip).

It would be a great explanation if it's a duff battery. MG diagnostics in Edinburgh currently have a 3 month wait list...

Thanks.

What actual current?

I think I misunderstood this! The charger is 5Amps.

 

[Alb]

Is your car actually an EV?

 

[hmadsen]

These batteries does not like to be deeply discharged, if you run the car so infrequently that the voltage goes really low, then you damage the battery.

That being said, it sounds like the battery you got was a dud.

If you had it on a charger that can do AGM specifically until the charger ended the cycle and it still had below 12V, that battery is knackered and a few deep discharges should not do that.

If the car is used this infrequently and you have the posibility of charging in your own driveway, if it were me, i would get some sort of DC socket mounted and have it plugged into a 12V battery charger (Think something like in the old days, when people used block heaters that were connected to the grid...230V directly back then, but the principle is the same)

 

[CallMeDave]

Is your car actually an EV?

Yes. Electricity goes in the front and vroom vroom comes out the back.

The drive battery has no issue holding a charge (according to the dash readout).

 

[Coulomb]

I charged it for 6 hours which was long enough for the indicator to go completely green plus an extra ~hour.

Ok, so that's roughly 30Ah (5A x 6h), and the indicator went green (likely indicating that the charge reached absorb voltage), and you gave it something like an hour to absorb. Assuming that the Noco isn't faulty, that certainly sounds like the 12V battery should be close to fully charged.

Hopefully the Noco does a little temperature compensation; lead acid needs to be charged to a higher voltage than normal when it's cold. You seem to have done this charging outside of the car, was this in a heated garage/workshop or still basically at freezing temperature?

It's certainly pointing to a bad 12V battery at this point.

 

[Steptoe]

The OEM MK 1 battery is lead/acid so can be replaced with similar so avoiding the extra complexity of charging to AGM (yes, I'm aware that all supplier websites do recommend replacing with an AGM stop/start type....upselling? lol )

 

[Coulomb]

The OEM MK 1 battery is lead/acid so can be replaced with similar so avoiding the extra complexity of charging to AGM...

But AGM is lead acid, just a different arrangement of the "plates".

Also, what complexity? They come in the same sizes, and drop in place. I'm not aware of any changes that are recommended.

The main difference is that they are a little dearer to buy, but seem to last longer in an EV application, so there is a similar or even lower long-term cost, depending on several factors.

 

[hmadsen]

But AGM is lead acid, just a different arrangement of the "plates".

Also, what complexity? They come in the same sizes, and drop in place. I'm not aware of any changes that are recommended.

The main difference is that they are a little dearer to buy, but seem to last longer in an EV application, so there is a similar or even lower long-term cost, depending on several factors.

I think AGM was more or less specifically invented/designed to be used in cars with STOP/START technology, the main advantage being that it has a lower internal resistance, making it more suitable, specifically for more frequent activations of the starter motor.

As such I don't think there are any drawbacks to an AGM battery in an EV, but since an EV has none of the very large current draws because it has no starter motor, I don't see it having any benefits as such.

Some manufacturers of EV's have disposed of the heavy lead acid LV battery altogether, and replaced it with Lithium ion batteries. Tesla for example have replaced it with a small 7 amp·hour Li-Ion battery, but they also actively monitor the SoC of that battery and the car can itself switch on the HV battery even if the car is "asleep" and parked up.

The main reason for the need for a large amp·hour battery in the ZS EV I would guess is down to it not "topping up" the LV battery so needs more juice to not run dry as fast, when parked up.

 

[CallMeDave]

Hopefully the Noco does a little temperature compensation; lead acid needs to be charged to a higher voltage than normal when it's cold. You seem to have done this charging outside of the car, was this in a heated garage/workshop or still basically at freezing temperature?

According to the blurb: "Avoids under-charging in cold weather down to -4°F and avoids over-charging in hot weather up to 104°F".

The battery was disconnected but still sitting in the engine bay.
I don't have a suitable heated space for it. I have 2 young kids so bringing it in the house isn't ideal. I could bring it in after they go to bed and try a top up charge and repeat reading at room temperature tonight.

The OEM MK 1 battery is lead/acid so can be replaced with similar so avoiding the extra complexity of charging to AGM

My car came with an AGM. Unclear if this was from manufacture or if the previous owner had replaced it.

Thanks everyone. Fingers crossed this will be a complaint to Halfords rather than a 3 month wait for an inspection and a fight over the warranty.
It honestly never crossed my mind that a brand new battery from a big name retailer could be unusable.

 

[Coulomb]

As such I don't think there are any drawbacks to an AGM battery in an EV, but since an EV has none of the very large current draws because it has no starter motor, I don't see it having any benefits as such.

My understanding is that the AGM batteries are better at absorbing power from the DC-DC in a short period of time. So if the car doesn't charge the 12 V battery for very long, or if the user makes many short trips, the AGM fares better. They also seem to degrade less with deeper discharges.

It should not matter much if the car tops up the 12 V battery when parked and asleep.

 

[Coulomb]

It honestly never crossed my mind that a brand new battery from a big name retailer could be unusable.

The staff at the retailer likely have no clue how to manage and look after lead acid batteries. Even though AGM will likely last longer on the shelf.

 

[Lovemyev]

For a 12 volt battery to perform and dependably operate correctly each and every single time, it has to satisfy both of these TWO tasks.
Prove / establish it can receive / accept a charge and then equally important, hold / retain that charge when the battery is left dormant over a period of time ?.
Generally 12 volt batteries do NOT deplete completely without a reason.
Some really good advice offered above, you could double check on the following items.
( 1 ) Clarify IF the battery IS capable of accepting a genuine FULL 100% charge and then confirmed status with a volt meter, a few hours after the battery has been left to sit idle.
Over the next few days of none use, with one of battery terminals still disconnected.
( 2 ) Confirm that the voltage reading is STILL displaying the same voltage on the meter, that it did a few days ago ?.
If there IS a sizeable drop, then this has just clarified that the battery is defective and should be exchanged with replacement unit.
However if on the other hand, the battery is showing no sizeable drop in the readings after a few more days have passed, then it appears it IS holding a charge.
Now try reconnect the battery and repeat the test process again, after few more days.
If now the battery voltage has dropped, then there has to be a parasitic drain in the car somewhere.

 

[pollenface]

It worked without issue. We use it infrequently (2 or 3 times per month).

So, did I replace a dud battery with a brand new dud battery? Seems improbable.

I think you're not using the car enough which is killing the 12V battery. Regular driving allows for regular charging which prevents sulphation (capacity loss). The solution is a simple 12V maintenance charger.

 

[Tim Green]

ICE cars also suffer battery problems if left for weeks without use, mainly due to alarms and other continuous battery loads.
The solution is obviously a maintenance charger, but this is only possible if mains power is close and there are no issues with cables, etc.
Another option could be a PV panel and charge controller- I use one for my 1950 MG TD and it works very well for the long periods when the car is unused in a remote garage. For the ZS, it may be enough to put the PV panel under tbe windscreen?

 

[BOB353]

Just get out and drive it more