Battery failure

[Fredbassett]

I bought a 2022 Jazz SR  a week ago and used it for the first time today. I got 500 yards from home and it died on me going around a roundabout! The screen went blank and pushing the accelerator did nothing. After a minute of pressing the power button a few times it started to move again. I immediately returned home and checked the 12v battery with a voltmeter. It read 8v. I assume the battery is dead. However, it had managed to start the traction battery at the beginning of my journey. My question is why did allow me to drive it if there wasn’t enough power in the 12v battery? It was incredibly dangerous cutting out like that on the road. A battery state of charge meter on the screen for the 12v system would be more useful then the one for the traction battery.

[Pine]

Let us know how you get on when you have a new 12v battery.

[Kremmen]

It surely has to be the 12v battery ?

Once you got the engine started it would have set the HV battery to start charging the 12v at about 14v so dying whilst driving must be failure

[Jazzik]

Go to a dealer and have the error codes scanned. It is virtually impossible stalling like this to be caused by the 12-volt battery once the car was in "ready" mode and driving.
Mind you: I am not saying that the 12-volt battery cannot be a bit less "healthy" after 4 years.

[jaytee]

 When I bought mine , 3 years old also, the battery was replaced by the dealer,but i think it had been unused for  a few weeks/months, the 12v battery is  small and it  can be run down  quite quickly if not  in use .

[coldstart]

I bought a 2022 Jazz SR  a week ago...

As it is a pre-facelift model: Have you checked, if the car has had the brake simulator issue fixed already?

[Jazzfan49]

I bought a 2022 Jazz SR  a week ago...

As it is a pre-facelift model: Have you checked, if the car has had the brake simulator issue fixed already?

Mine is a 2023 pre facelift SR version, my dealer confirmed that it does not require the brake simulator replacement, I hit a pothole recently and burst a rear tyre the 12v battery lasted less than an hour with hazard warning lights on so had to be jump started by the RAC recovery engineer, tyre too badly damaged to use the emergency repair kit so they fitted an emergency space saver wheel to get me home.
 

[Kremmen]

Sounds like the trick may have been to start EV mode every now and again to recharge the 12v battery

[coldstart]

... and checked the 12v battery with a voltmeter. It read 8v. I assume the battery is dead. However, it had managed to start the traction battery at the beginning of my journey. My question is why did allow me to drive it if there wasn’t enough power in the 12v battery? ...

Do you remember whether the green "ready" indicator (the car with the two-pointed arrow below it) has been lit?
If both the HV (aka traction) battery as well as the 12V battery have been only marginally charged when you took off and the car wasn't signalling "ready" might explain why it "died" on you.

Has this happened again?

[CB72]

Is this battery problem ever going to be sorted, the Yaris has the same problem. Just putting a normal battery in the car might help. An ICE car can sit in the garage for ten years and still start. Isn't there a way to use the EV battery start the car when the 12v battery fails, I think there is a car that can do this, can't remember the model.

[coldstart]

... Isn't there a way to use the EV battery start the car when the 12v battery fails, I think there is a car that can do this, can't remember the model.

For security reasons the HV system gets completely shutdown when the car is turned off.
The 12V battery is essential to prime the HV system which then in turn cranks the ICE.

Even putting in a "normal" 12V battery as per your suggestion wouldn't cure the root cause (only delay its effects), mainly: Driving the car only sporadically and/or only for short distances which will eventually result in a depleted 12V battery.

If you have this kind of motion profile you wouldn't even get great fuel benefits from the (quite elaborate!) e:HEV drive train because the engine never really gets out of cold start conditions.
A true EV would be the better and more "fuel"-efficient choice for such a use case (but would probably suffer from an occasionally depleted 12V battery as well).

[Kremmen]

The draw on the 12v battery must be significant when the car is off and left for just a few weeks to deplete it

I know it's totally different but I've got smart devices round my house that are continually transmitting data that run for over a year on a couple of AAA batteries

I also remember my dad's A35 van that had a red/white light hung on the drivers windows top that was illuminated all night, as was often done in the 50's and 60's, and the van started without issue every morning

Imagine having a normal filament bulb wired to the Jazz 12v battery all night, it would surely flatten it

[Lord Voltermore]

Isn't there a way to use the EV battery start the car when the 12v battery fails, I think there is a car that can do this, can't remember the model.

I think there are one or two makes that have an override switch  which, in an emergency,   takes a  supply from the high voltage battery ,converted to 12volts. .  But some owners would continue to use this  override switch over a long period  rather than  go to the trouble and expense of replacing a faulty 12v battery  . Or in the event of the car not starting or behaving as expected  they  might , in desperation ,repeatedly activate the overide often enough to discharge the VERY expensive HV battery to the point that causes it damage.

[CB72]

Hyundai and Kia have a battery reset button, once pressed you have to wait 30mins before starting the car, also you have to manually open the doors, not something you would want to do very often. You'd be off to the garage quickly if that happened regularly.

[coldstart]

The draw on the 12v battery must be significant when the car is off and left for just a few weeks to deplete it ...

You are absolutely right when (or if? - the english language just has too many words for the "same" thing) the 12V battery was fully charged at the beginning!
(which it probably wasn't, if the car wasn't "active" for longer periods in the past)