Low voltage battery discharging

[Nickel]

Car is a ZS Trophy LR, just under a year old.

We have started seeing messages that the "Low voltage battery needs charging, do not leave car more than 3 days unused." Or words to that effect.

Yesterday evening we parked up with the battery registering 13.8V. Later in the evening it was down to 13.0V, measured via the MG Smart app.

Now (lunchtime), it's down to 12.2V.

As far as we can tell, nothing we control is on. And the car hasn't been used since we parked.

Can anyone shed any light?

Nick

 

[Nicko]

I've had identical problems.
In for first service this week
Asked dealer to check battery.
Tells me it's healthy and that my problem is I'm not doing sufficient mileage!!!
I told him I didn't read any warnings when buying the car that it was only suitable for high mileage driving!!!
Not happy.
His solution was to sit for 15min every day in drive mode before leaving my drive. He says the battery system is the same for all makes of EVs.

I have done less than 5k and mine is just over a year old. Who did you buy the car from? I bought from Nathaniel's and I had the latest updates with no problems.

 

[Pontyboy]

I bought from Nathaniel Cars Cardiff.
My mileage is under 4k
What was the update related to?

 

[Nicko]

I bought from Nathaniel Cars Cardiff.
My mileage is under 4k
What was the update related to?

On my Trophy Connect the update is R22. Do you use the car daily? I do because I use it for work and take the dog for walks. They might be saying it is standing for a while?

 

[Lovemyev]

Update to my previous post. Car checked by dealer and as previously indicted by others, no problems found. They have asked that I keep a log of any warning messages on displays and keep an eye battery state. Did state that the chances are it will happen again, maybe one,two, five,ten days, weeks etc. Stated they are carrying out all sorts of tests to identify problem...are pretty confident the prob lies within the infotainment system but unable to pin down at moment. Asked how many of this problem type this year..60 was answer and that's just one dealership!!!

While they are still faffing about conducting their studies, you could be getting a lift from the recovery services - brilliantly reassuring !.
Top tip :- Purchase a booster pack and store it under the drivers seat !.
Trust me, it’s a worth while investment.
If you want to take it a step further, you may consider fitting a 12 volt battery monitor onto your battery.
It will keep tabs on the SOC of the battery and send a notification to your phone if it detects the battery is running too low.
Simple to fit and it offers a historical list of the health of the battery.
About £22 on Amazon I think .

 

[Nickel]

As the OP, I thought I'd update my situation.

As I said upthread, I took the car to our dealers, but they couldn't find anything wrong. That was a Wednesday. On the Friday, we had a 12V battery warning again. So I took it to the dealer again, as we were off on holiday on the Saturday.

The battery still checked out OK as far as they were concerned, but they took it more seriously this time and gave me some advice on what to do if I had problems.

We charged the car to 100% overnight Friday, and set off on a three and a half hour drive to our holiday let. Charged it (this time to 80%) at our destination overnight Saturday and drove about 20 miles return for a Sunday lunch, then parked up.

I was watching on the BM2 (no mobile signal to use iSmart) and it was clearly decaying, from 13V on Sunday to 11.5V (I think ) on Tuesday evening. Wednesday morning, it was dead.

Using the advice from here and having been told now to use the emergency key by the dealer, we got in and used our booster pack to start the car. Happiness all round. But Wednesday evening and Thursday, it was decaying again.

On Friday, it was down, but started. When we returned after our day out, a visiting car was in the spot we usually use, and so I parked a car length or so away.

Our battery has been fine ever since.

I have two theories but would happily accept anyone else's thoughts:

1) The mobile signal in North Devon is pants at best and where we were is next to non-existent. I am wondering if the car was trying to establish a mobile internet connection and draining the battery in the process. When I relocated the car, perhaps there was enough signal in the new spot to stop this happening.

2)We are not routine high mileage drivers any more. Normal shopping/pub/restaurant journeys are perhaps 3 or 4 miles each way with slightly longer trips to friends and occasional 160 mile trips to our son's family. With the increased charging intervals on a LR model, as compared to the Mk1, perhaps we are not fully recharging the 12v battery and it wasn't recovering. And perhaps we have finally charged it properly.

The car goes for its first service on Wednesday and the plan is for them to do a capacity test, as the 12v warranty runs out 4 days later. My gut feeling is that the battery is fine and the problem is the demands placed on it. But we'll see.

 

[scoobeesnac]

That’s an interesting fact - we also had very poor/no mobile signal when our 12v discharged.

MG will be updating our Tbox (Telecoms) soon to try and get it working again - they tell me it’s rather out of date, so hopefully the update will resolve any issues.

 

[Lovemyev]

Your usual small shorter trips are a factor and now the car has been active on the much longer journey of three hours, I suspect the 12 volt battery has had time to fully recover.
Returning back to your usual routine of short trips and the onset of colder weather may cause the issue to return.
A helping hand with a 12 smart charger every so often could be something worth considering ??.
A 12 volt battery in a good state of health should be able to tolerate a number of shorter trips though.
A capacity check is a good way forward.
Disconnecting the battery and then fully charging it, then checking it with a meter.
Then leave it stand over night, then recheck to see if there is any reduction.
This is important.
The car could also be checked for any type of parasitic drain.

 

[Tim Green]

Most garages used to have battery load testers, which were a foot long resistor capable of dissipating a lot of heat. This was applied across the battery terminals (do NOT try this at home!) and was supposed to be definitive test of a faulty battery. Not sure if Halfords have the testers (for in-house use?)

 

[Gadget Geek]

When I had my Kona, the 12V failed without warning and left me stranded at a supermarket car park. The AA came and used a battery pack to get me started. I drove to the dealership, switched off to go inside, and when the tech came out to look at it, it was dead again. He put a load across the terminals and there was nothing there. Fortunately, it was a month inside the warranty and got it changed for free.

 

[Coulomb]

Yesterday evening we parked up with the battery registering 13.8V.

13.8 V is the float voltage for lead acid. That's a voltage that the battery can happily "coast" at without over-charging, but it has to be pushed up that high: either charged from an external car charger or the car's DC-DC, or it's settling towards a resting voltage after having been charged in the last (very roughly) hour or two. So you can't use any voltage over about 12.8 - 13.0 V (depending on exact chemistry, temperature, and perhaps a few other factors) as any sort of indication of the state of charge (SoC) of the auxiliary battery.

Later in the evening it was down to 13.0V, measured via the MG Smart app.

In other words, later that evening it was pretty much at 100% SoC. It's full.

Now (lunchtime), it's down to 12.2V.

12.0 V in a nominally 12 V battery is close to dead flat, perhaps 20% SoC at most. 12.2 V, depending on many factors again, indicates a low, but not drastically low, voltage, but ONLY if it's been resting (next to no load or charge for hours). If you're measuring this in the car having opened the doors, then all sorts of computers have woken up, you may have some lights on, and if you use the start button to turn the car on (so you can see the 12 V reading on a screen for example), then radio, screens, perhaps the blower, and many more computers.

To meaningfully compare SoC (e.g. to see if the battery has self-discharge, or perhaps there is a "phantom" auxiliary battery drain), then you really need one of those battery monitors, or perhaps leads accessible outside the car to connect to a multimeter without opening a door, and not even approaching with car keys in your pocket. The car keys will probably wake up the body computer.

1) The mobile signal in North Devon is pants at best and where we were is next to non-existent. I am wondering if the car was trying to establish a mobile internet connection and draining the battery in the process.

That's an interesting theory, for sure. I'm doubtful, but I certainly would not rule it out.

 

[Coulomb]

Disconnecting the battery and then fully charging it, then checking it with a meter.
Then leave it stand over night, then recheck to see if there is any reduction.

That's a great way to check for self-discharge. If it doesn't seem to have significant self-discharge and yet it runs down in the car, that's a pretty good indication that it's getting loaded by something in the car.

I note that cars can take 5 minutes or more to fully sleep all their computers, apart from small parts of the ones that have to sense for keys or commands over the cellular network. So the drain will never be zero, unlike your grandfather's car that just had starter, wipers, a few lights, and maybe a horn. But it should be under about 100 mA (0.1 A, a tenth of one amp).

 

[Coulomb]

Most garages used to have battery load testers, which were a foot long resistor capable of dissipating a lot of heat.

I suspect that with the (eventual, at least in Australia) proliferation of EVs, carbon pile (or more modern equivalent) testers might become more common. In an Internal Combustion Engine car, you get early warning that the auxiliary battery is dying, as you perform a ≈200 A load test (albeit brief) every time you crank it. An EV just has to power some computers and pull in the contactors, maybe 5% of the starter motor current. Then it gets to loaf along as the DC-DC does all the work.

Fellow old fogies: note the 6 V option at the bottom, and the classic old-style radio knobs.

Fellow electrically savvy people: how long do you recon that those cables would last at 1000 A? Two whole seconds? 0.2?