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I emailed and had a very prompt reply from Jemma. Apparently they have no concerns regards the battery. “Our technical team have confirmed that there are currently no concerns regarding the 12V battery fitted in the Kona electric, however we constantly monitor any reoccurring issues that are brought to our attention”.

They commented that, “It is impossible for us to guarantee that the many complex parts that go into the build of our cars will never fail” I pointed out that the lead acid battery invented in 1856 is not exactly complex


I did mention, that as a Which member I had completed their annual survey and whilst I raved over the Kona I had reported the 12v battery failure. If anyone has any concerns, better report them.
 

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I've been doing some logging of aux battery voltage (with Torque Pro) while in "run" mode and charging mode. What I'm seeing in both cases is that initially the aux battery is charged at 14.7 V for some minutes with decreasing current typical of charging a lead-acid battery.
After that charge period in "run" mode the average current going into the battery drops to zero but it does dither back and forth quite a bit, seemingly acting like a capacitor on the 12V system. The average voltage reported during this period is 13.0 V but it does dither slightly to higher levels. Continuing on, it's not clear yet after what period the aux battery charging continues.

In charging mode (trickle) the average current after the initial aux charge period is stable and also near zero. The battery voltage sits at 13.0-ish, same as above.
I've verified that the TP voltage reading data matches the aux battery terminal reading within an impressive +/- 0.01V.

What I'm seeing is that the battery is not charged all the time. But when it is, it's at a whopping 14.7 V.
The puzzle here is how is it possible to read 13.0 V unless that is the actual "12V system" voltage? If that is the case, I'll speculate that the current shunt on the aux battery negative terminal is used to regulate the LDC output voltage (in real time) such that the 12V system voltage suits both the periodic charging schedule of the aux battery and the immediate 12V system loads.

It's not yet clear on what basis the aux battery is charged and whether that's based on the battery terminal voltage (which it knows by the LDC setting a system voltage that produces zero current through the shunt) or a time schedule, or any other factors.
 

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12 volt battery problems are also common in the Ioniq, although I have not experienced a problem myself. It seems to be a Hyundai problem rather than with a specific model.
 

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The lady I spoke to (Mel) did confirm that their technical team is aware of battery issues but they have been "solved" by disconnecting dashcams... which is obviously wrong, but at least it means they are clearly getting reports back of 12V batteries going flat. That's the first battle!
 

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I'm thinking of running my dash cam off a small 12 Volt back up battery so that it can run all the time like sentry mode in the Model 3. Burglar alarm batteries are ideal for the job.
 

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The lady I spoke to (Mel) did confirm that their technical team is aware of battery issues but they have been "solved" by disconnecting dashcams... which is obviously wrong, but at least it means they are clearly getting reports back of 12V batteries going flat. That's the first battle!
If the dashcams are running in parking mode it is possible they are running down the relatively small capacity 45ah battery to the point of failure. Most better dashcams allow you set a power cut out once you reach a preset voltage level. That said I still had my 12v battery go flat despite my dash cam being powered through a separate lithium battery in my glove box.
 

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Just to let you know: after 5th visit to dealership (and probably 10 battery failures) Hyundai decided to replace 12v battery. I'm quite sure problems will disappear (at least for some time based on @Electra Glide in Blue experience).

Hyundai still couldn't find any issue (including the battery they load tested many times) but hopefully battery replacement will make the car reliable again.
 

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All I can add to the conversation is what I've learned from voltage and current logging, while driving and while unused for the past week or two, in ambient temps of 16 to 22 C.
1) The 12V battery charges for about 10 minutes after each entry into Run, Utility or charging modes, then subsequently is left alone for the duration of that mode with no net current draw. Charge voltage is around 14.7 V.
2) Unlocking and locking, opening doors, powering on without entering the modes mentioned above all draw charge from the battery, as does the off-peak charge timer as the 'on' time approaches.
3) If you don't use the car for 24 hours it will initiate the aux battery saver (if enabled), charge for 15 minutes and repeat that every 24.25 hours. It's unclear if it adjusts this charge period to maintain the battery, counter added parasitic drains or adjust for temperature.
4) The system has an Intelligent Battery Sensor (on the GND terminal) that allows precise measurement and control of voltage and current. It seems to be similar to the Prius, based on a video from the Weber Auto YouTube channel.
I've seen one incident of the car doing what I can only speculate was a 4-minute load test on the battery during Run, immediately after the charge event.
 

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The last week or so I've noticed my voltage running lower for extended times. It used to nearly always be mid 14s but now I often see 12.9 or 13.4.

Today after I put it in the garage and locked it I noticed the PNDR buttons were still lit blue and the orange P light was on, which I've not noticed before. Still on a few minutes later, so I unlocked, started, stopped and relocked ... same. An hour or so later they'd gone out.
Is that normal?
If not I wonder if this is leading to a "problem with the 12V battery".
 

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The last week or so I've noticed my voltage running lower for extended times. It used to nearly always be mid 14s but now I often see 12.9 or 13.4.

Today after I put it in the garage and locked it I noticed the PNDR buttons were still lit blue and the orange P light was on, which I've not noticed before. Still on a few minutes later, so I unlocked, started, stopped and relocked ... same. An hour or so later they'd gone out.
Is that normal?
If not I wonder if this is leading to a "problem with the 12V battery".
That is normal. Always has been like that for me.
 

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While charging it should be around 14.65 V. That may be affected with temperature compensation that I haven't encountered during our summer.
  • It only charges for around 10-20 minutes at the start of each driving or charging event.
  • Same with aux battery saver events which trigger daily once the first 24 h period has elapsed after the last proper drive, meaning over about 20 min. Shorter drives, moving the car, opening a door, or entering Run mode to check something doesn't reset the trigger or disrupt that schedule.
While parked it will should start from a peak around 13.1 and drop slowly due to quiescent draw, normally to around 12.8 before the next aux saver event kicks in. That seems to be the period where dead battery problems can arise as the aux saver doesn't seem to be able to save itself if the voltage drops too low. There is new evidence from one of our fellow owners that each charging period doesn't compensate for prior higher losses so I would speculate that losses due to abnormal current draw can accumulate over several days if the car is parked and relying solely on the unfortunately-named aux battery saver. Eventually the voltage will be too low for the systems to operate.

While driving or charging past the "charge" period of 10-20 min, the system voltage will suddenly drop and dither just above 13 V for the duration of the trip (or charge) as the system (LDC) maintains a high-enough voltage as to draw effectively nothing from the aux battery. That system voltage is quite noisy so don't rely on random spot checks. 12.9 to 13.4 sounds perfectly normal for this period.
 

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I just wanted to update you all on issues with flat 12v battery.
Same as @Electra Glide in Blue I had increasing number of days with dead battery. After 4th or 5th visit Huyndai finally replaced the battery (although they tested old one many times and said it is fine).
It has been 3 weeks now after replacement and not a single issue with 12v system so far. So it looks like either: original battery was faulty to some extent (strange as it worked normally for first year) or something is causing battery degradation.
 

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Since the dealership fully recharged my 12V battery overnight, I've not had any problems. I think this is a long term problem where it slowly but surely drops on average, until it simply gets too low.
 

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I have just watched the Fully Charged episodes featuring Chelsea Sexton and the 1990’s GM EV1. What an incredible car, I recommend watching. Anyway, back to the point, this car had a button hidden under the dash and if you could not start the car you could press this button and it would put enough charge in the 12v battery to start the car and apparently Hyundai amongst others are now going to do this! Does anyone know anything more about this?

It seems incredible that such a simple feature like this from 30 years ago got forgotten. When I had a flat 12v battery and the HV battery was at 70% charge it was very frustrating that a 15month old 12v battery did not have enough voltage to start the car.
 

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I saw that video too. What an obvious idea to charge the 12V from the traction battery. A bit of a "DOH!" and a forehead slapping moment for the designers. :)
 

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I propose a simple challenge, sketched out below.

1 Use a low power comparator/ op-amp as a voltage sensor to detect when the 12V battery voltage falls below about 11V.
This will be connected across the 12v battery terminals and take a current of a milliamp or so.

2 The comparator/op-amp output signal turns on a simple bipolar transitor switch, which in the ON state activates a wireless doorbell sender, ie acts as if the door bell button has been pushed.
These door bell transmitters typically are powered by their own CR 2032 cell or similar.

3 The remote (indoor) chime sounder warns when the +12v battery voltage is low.
 
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