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Cells that are out of order are considered broken and that is not considered to fall under degradation and its 70% rule; therefore they are just replaced under battery warranty.
 
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So I got the battery health report from my local dealership. (Free of charge of course). It's shows 87 cells at 4.06V - 4.08V and single cell at 3.86V. This was at 89% indicated SoC after a full charge and 15 mile journey.

They said it's not bad enough to do anything about, but I got the impression that if I make enough noise about it they'll do a longer investigation. They said generally they class a bad cell as being over 0.5V different to the others.

Does anyone have in-depth experience of these big battery packs and can help me work out what to do next?

I suspect that if it was at 100% SoC that bad cell would be further away, but I'm not sure. Maybe it's time to look up the OBD thread and keep a closer eye myself!
 

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Why didn't they measure it at 100% SoC? I would indeed expect the most serious differences then. Is there a reason for the choice of exactly 89%? They should make that choice of a % between 0 and 100% deliberately and 89% looks rather arbitrary; so I would not be satisfied without knowing their reasons.

By the way, suppose the cell voltages at 100% are 4.2 V, and the out of order cell still has 3.86 V, then still their criterion of 0.5 V difference leaves you empty-handed. You have to promise them that you will return every month to let them check the cells again and again, because there may be a good chance that this 3.86 V will decrease fast so that you fulfill their criterion soon.
 

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I'm under the impression that classic Ioniq has all the cells balanced close to millivolts of each other not 0,02 volts. It is quite a quality drop if the facelift has such big tolerances! On top of that one cell can be so badly damaged that it can vary 0,49 volts from other cells.
 

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Why didn't they measure it at 100% SoC?
I have the same question in mind. I think the mechanic didn't really understand what they were doing. So I've contacted Hyundai UK customer support to ask for support on the issue.

It was at 89% when I arrived at the garage. They didn't bother to charge it, they just checked the cell voltages.
 

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I'm under the impression that classic Ioniq has all the cells balanced close to millivolts of each other not 0,02 volts. It is quite a quality drop if the facelift has such big tolerances! On top of that one cell can be so badly damaged that it can vary 0,49 volts from other cells.
To be fair, 0.02V is 20mV. So it's pretty close on all the other cells. It could be an ADC issue where it only measures in increments of 0.02V for that particular view.

I agree that 0.5V seems like a big differentce to be their threshold for doing anything about it. I'll keep you all updated!
 

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So I got the battery health report from my local dealership. (Free of charge of course). It's shows 87 cells at 4.06V - 4.08V and single cell at 3.86V. This was at 89% indicated SoC after a full charge and 15 mile journey.

They said it's not bad enough to do anything about, but I got the impression that if I make enough noise about it they'll do a longer investigation. They said generally they class a bad cell as being over 0.5V different to the others.

Does anyone have in-depth experience of these big battery packs and can help me work out what to do next?

I suspect that if it was at 100% SoC that bad cell would be further away, but I'm not sure. Maybe it's time to look up the OBD thread and keep a closer eye myself!
There seems to be a battery manufacturing defect that occasionally impacts the 64kWh Kona Electric where a single bad cell severely impacts the range. I believe the 38kWh Ioniq use the same LG Chem battery cells. See this German thread for some more details. Drastischer Einbruch der Reichweite um gut 30% - Akku zeigt 100% - lädt aber nur effektiv rund 70% - Kona - Batterie, Reichweite • Hyundai Kona Elektro - Elektroauto Forum
This is not deterioration it is happening in new cars. I have heard similar reports from both Canada and Korea for the Kona, but this is the first one for the Ioniq.
 

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There still was a similar report for the 38 kWh Ioniq by Packard here at July 5. I quote (after applying Google Translate) this post:
Hi. After a long search I have now found the right posts. I have the same problem: I also wanted to load to 100% for balancing reasons - as described in the manual - and was then amazed at the very reduced range. OBD2 dongle in and EVNotify interviewed. And lo and behold: SoC display 100%, SoC BMS 74%, SoH 100%. Tried different things like driving completely empty and fully loading CCS again. Here too, premature reduction in charging capacity. The individual stages of the charging curve have been reduced by approximately 25% beforehand. The friendly Hyundai dealer was really friendly and read everything first. And then "deleted something from the error memory". Probably this error that always appears. And: has brought nothing. Now the apparently only knower (I'm really not sure ...) is on vacation for now. Me too. So everything is ok. Let's see what comes next. At least it is confirmed to me here that I am quite right in my assumption of a defective cell (car scanner shows strange values). Very annoying!!!
Oh yes: my car now has 12,500 KM "down" and is a ... IONIQ FL !. So far for that ...
And anticipating: otherwise I am very satisfied with the conscious choice of "FL" instead of a vFL or even TM3. Hope everyone get well soon
 
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You could roughly estimate for Packard quoted above (from Soc BMS 74% vs SoC display 100%) a loss of usable capacity of around 25%. Consider Knifyspoony's post:
...
E.g. 130 miles at 4.8 miles / kWh discharges from 100% to 8%.
130 ÷ 4.8 = 27 kWh used
Adjust for 8% remaining:
27 ÷ 0.92 = 29.4 kWh full discharge
....
If I calculate 29.4/38.3, this is 77%, so also a loss of around 25%. These two cases have much in common.
 
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Similar problems reported here for the Kona EV were addressed by replacing the full battery; see in particular this post of Friedmar:

I had this problem too. It took about 4 months until the battery was completely replaced. Plus about 6 visits to the dealer over several days. The duration was due to the fact that a) the dealer needed a special crane for the workshop, the battery weighs approx. 500 kg and b) the replacement battery had to come from Kore by ship. Flying is not!

After replacing the battery, another workshop visit was due because another part had to be replaced.

Now everything seems to be OK. Current range at 90% 420km. I'm happy with that.

I am still satisfied with my dealer. Hyundai well, on my complaint that I could not use the car as intended for over 3 months, no trips over 100 km due to insufficient range and practically no charging power. Fall from approx. 20 kW to less than 5 kW after approx. 10 minutes. And that at a 50 kW station. Charging was only possible on 22kW columns with charging power below 5 kW! I am still waiting for an answer or compensation after another 3 months.

Kind regards
Friedmar
Maybe you can show this to your dealer, @Knifyspoony.
 
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Thanks Jan and JejuSoul for your examples. I'll keep you all updated with my Hyundai UK and local dealer interactions! I'm hoping to hear back from Hyundai UK this week from a customer service enquiry I've raised.
 

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That's great to see you can actually see which cell is the bad one (Cell 32). I use just the free lite version, that also shows the cell voltages and temps. So far so good, all in perfect sync for a 2+ year old battery.

Hope you get it sorted, keep us up to date! Make some noise on Twitter / Facebook on their pages if they don't sort you out, and they soon will.
 

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I've now done a long journey (and warranted a 100% charge) since having the OBD reader. See attached for the cell voltages at 100% displayed state of charge. Max 4.16V, Min 3.92V. I also have data down to 20% displayed SoC if anyone's interested. But my bad cell seems to be causing the problems at the top end. According to my app: 100% displayed SoC equated to 76% "Real" SoC. I know there's a margin at the top, but it shouldn't be that much!

Does anyone have equivalent data from a "good" battery about exact cell voltages at 100% and "real" SoC?
 

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Lce sont les tensions d'une batterie en bonne santé, ioniq 28 du 11/2018, 28700km.
Thanks Redfast. Interesting to see that 4.14V seems to be the top voltage. Does anyone have data from a 2020 Ioniq to add to this?
 

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In fact I noticed 3 types of full charge which shows 100% on the ioniq, and 95% of the BMS on canioniq or EVNotify. 1st type: cells between 4.12V and 4.14V. Unbalanced battery 2nd type: all cells at 4.14V except 1 possibly at 4.12V. Balanced battery. 3rd type: all cells at 4.16V except 1 possibly at 4.14V: balanced battery. 1st type we have a total of about 25kWh in total useful capacity. 2nd type we have a total of around 26.2kWh of useful capacity. 3rd type we have a total of about 27kWh of useful capacity. In all 3 cases, the ioniq displays 100% and canioniq type software 95% BMS. It means that the percentage does not mean much specific. Only canioniq or EVNotify give a precise capacitance by voltage. I never managed to reach 400V without having taken care to balance with a few slow loads close together (whether in 10A, 12A and 16A I did all 3). I peaked at 397.5V at each full charge so 25.3kWh maximum capacity. It demonstrates the utility of balancing your cells with slow charging to maintain battery health. Small detail, do not hesitate to do a full maintenance charge to leave for a low or very low battery charge (I even started from 1% during my last maintenance charge, that is to say ... ).
 

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That's some useful info Refast. I think my bad cell is beyond a balance charge - the car seems to be trying to bring it up but the bad one never goes above 3.92V. It's going back to the dealership next week for a week-long investigation.

Interestingly, the ECU still says it's all 100% State of Health. But I have noticeably less capacity.
 
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