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I'm buying a really nice 2018 Ioniq 28 kwh Premium in a few weeks and I asked them to get the battery checked at the dealer.

I'm not sure exactly how to read this but the dealer said everything was fine.

Anything worrying in the printout?

thank you

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/Jim
 

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The circled values are the lowest and highest measuring cells in the pack. That they are equal to two decimal places is a good sign. You don't want to have batteries of differing voltages in your pack. The BMS (Battery Management System) will not allow the pack to be charged if any cell exceeds a maximum voltage, or discharge if any cell is less than a minimum voltage. That means that a single low voltage cell will prevent you from getting the maximum range of your car.

My wife's first Chevy Bolt (purchased used) had one cell that was about a quarter volt (250mV) lower than any of the others, and she could only get about 150 miles on the guess-o-meter. I discovered that the low cell was the cause when I plugged an OBDII dongle into the OBDII port under the dash, and looked at each of the 96 cells' voltages. We reported this to the dealer, and after some pushing on our part, got them to replace the battery pack (this was BEFORE the Bolt fires started being reported!). She has since done the GM buyback thing and gotten a new 2021 Bolt to replace it. She is expecting to get yet another new battery pack from GM!

Anyway, your max and min cells are showing as balanced. All is good! Hope this helps!
 

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Discussion Starter · #3 ·
Thank you, yes that really helps a lot! It's clearly a sign of a healthy battery pack.

I read somewhere that the Ioniq is designed to be able to switch out separate cells if they fail, that's a welldesigned piece of machinery.

/Jim
 

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Jim

Seems like the battery is good. But it would be better to test it after it's been driven a bit. From the read out it would seem that the battery was a high SoC. If they could let you drive it to about 50% SoC and do the test again, that would be best. As mentioned above, you're looking for a max cell voltage difference for an unloaded battery of 0.02V
 
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Values are good, cells have identical voltage. Actually, identical list of parameters can be read with cheap OBD2 dongle and a smartphone.

Battery degradation can only be assessed after driving the car to almost empty then charging to 100%. (using charger info and Cumulative Energy Charged in the app for calculation).
 

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The auxiliary battery voltage of 11.7V is way low, I'd see if you can get them to swap it out. If they won't do it, then be prepared to have to replace it out of your own pocket after you take possession of the car. Unfortunately it's not cheap. At an absolute minimum I'd have them take it out of the vehicle and run a recovery/desulphate cycle on it with a suitable smart charger before they hand over the car.
 

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If you divide the first value here by the advertised (not raw) Ah rating you can determine the full-charge charge cycle count. I think it's 78 Ah so that's 421 cycles accumulated. The cycle life alone is perhaps 1200 down to 80% SoH but time-based degradation will also factor in.
The power numbers can tell you within a small error the average battery cycle efficiency, for what that's worth, 11507/11980 = 96%. I think a new example could be closer to 98.

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KevinT - what you are probably referring to is resting voltage - measured without any load, after at least one hour of resting the 12v battery without putting any loads on (preferably several hours later).

This auxiliary battery voltage of 11.7V was measured under significant load of several amps, and probably after some minutes of testing (without putting the car in Ready mode), in such situation voltage will rapidly drop from around 12.5-12.7V to what was observed. You will see it in any car, both ICE or EV.

Generally, if car was sitting for weeks or months on dealer's lot, the 12v battery is often in bad shape. It is then advised to ask for a separate quick test of 12V battery with a dedicated 12V-battery tester (showing SOC and SOH of the 12V battery). But it is unrelated to battery voltage dropping under load lasting for several minutes to 11.7V or even less.
 

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This is fascinating info! I've bookmarked the link the link to this thread. For comparison, I'm posting my figures for my 2019-built 38 kWh.
I'm using EV Watchdog Free to read data from my Viecar 4.0 OBDII dongle.

All the screenshots were on 28 May 2022, car had been slow-charged to 100%, ending at 10:08 a.m. Car was then packed up during the day, & departed about 4 p.m.
Cell voltages were recorded at 10:08 after 100% SOC reached, then again at 3:51 p.m. and 3:56 p.m. Tiny 0.02V difference detected at 5:51, hence repeat reading at 3:56 when it had gone. Here are the stitched-together grabs, 10 a.m. followed by 4 p.m. pair.

10 a.m.
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Now the analysis, thanks to @KiwiME for his explanations above.
1) Average Battery Cycle Efficiency = (20.3/20.7) * 100% = 98%. Looks good.
But, does this figure fall as battery degradation happens? Or maybe it stays pretty constant but the capacity simply drops a bit?

2) Cumulative Charge Cycles done = 20700/120 = 172.5.

3) Lifetime Check.
38.3 kWh useable capacity * 172.5 Cycles = 6606.75 kWh provided by battery,
16874 miles / 6606.75 = 2.55 miles/kWh ! What's gone wrong? Should be more like 5! I can only assume this 172.5 Cycles is the effect of Regen doing about 1/2 the total charging of the battery? Would make sense, as Regen charging's no different to mains charging, and is cycling hence degrading the battery (v slowly!) in exactly the same way.
 

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The auxiliary battery voltage of 11.7V is way low, I'd see if you can get them to swap it out. If they won't do it, then be prepared to have to replace it out of your own pocket after you take possession of the car. Unfortunately it's not cheap. At an absolute minimum I'd have them take it out of the vehicle and run a recovery/desulphate cycle on it with a suitable smart charger before they hand over the car.
Yes the 12V is gone, needs a new one. They can not be refurbished to a condition lasting longer. You can boost them to look good for some days but won't do much. Like fixing rust with a rattle can :p:p
 

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This is fascinating info! I've bookmarked the link the link to this thread.

1) Average Battery Cycle Efficiency = (20.3/20.7) * 100% = 98%. Looks good.
But, does this figure fall as battery degradation happens? Or maybe it stays pretty constant but the capacity simply drops a bit?

2) Cumulative Charge Cycles done = 20700/120 = 172.5.

3) Lifetime Check.
... What's gone wrong? ...Would make sense, as Regen charging's no different to mains charging, and is cycling hence degrading the battery (v slowly!) in exactly the same way.
I'm always cautious of posting things like this because from experience it's usually ignored and my time is wasted. But I like analysing this stuff and that's partly why I bought an EV. I don't mind explaining it to anyone interested. Many things can be determined from those four cumulative Ah and kWh values, but you have to work them out yourself, as the BMS does. The BMS of course uses this info to figure out some of the things it needs.

As an analogy to the battery pack, if you imagine the battery to be a 100 litre tank of water attached to a pump/turbine via a restrictive pipe, you'll see more intuitively how this works. The tank has a "full" mark (100% SOC), an empty mark (0% SOC) and a starting level somewhere in-between, let's just say at the 52.5 L mark (SOCo = 52.5%).

We're going to assume that the pump is perfectly efficient in both directions, in other words 100% of the energy going in or out results in an exact equivalent pressure head change to the flow of water. We also have a flow sensor that can measure water volume as it passes in or out of the tank.

If you measure the water volume flowing in and out separately (Ah) you know that every time you pass the original water level at 52.5 L those numbers will be the same because water is not lost while in the tank. We'll assume of course that the water doesn't doesn't evaporate. "Coulombs" (Ah) doesn't either in a battery (at least as best as I'm aware!)

If you use the pump to raise the level from empty to full (adding up the energy needed to pump it in) and then exploit that water pressure to generate power (adding up the energy gained) as the water level drops back to empty, you can be sure sure that you will get less energy out than you put in because of losses in the intermediate restrictive pipe. The equivalent for battery pack losses is its internal resistance, which gets worse as it degrades.

Since the four cumulative values were zeroed at the same time (at the factory, or later after a BMS software update) you know that whenever the water level passes 52.5 L (SOCo) the ratio of the cumulative energy gained at the pump as water drains out to the cumulative energy lost required to pump the water into the tank represents the energy storage efficiency of the water tank. If our restrictive pipe was not present the efficiency would be 100%. See the first image below.

Technically you have to measure storage cycle efficiency of the tank (or battery) when it is at 52.5 L (SOCo), otherwise your result is in error by the difference in the current water level (charge level) from that when the values were all zero.

My Kona returned 98% efficiency some time ago, now 97.8%, see image. Note that my SOCo is 52.5%, a coincidence, lol! The 96% above is the first time I've seen anyone post values for an "older" EV and that seems to indicate that it does drop over time, and that's entirely expected based on Li-po datasheets.

Regarding your driving efficiency, since it's impractical to start and stop at the same exact SOC it's better to only look at the change in values over a trip of known distance. Read those four values at the start of a trip and again at the end. The net energy used is ΔCED - 0.98 x ΔCEC where 0.98 is your determined battery cycle efficiency applied to the regen. The net coulombs used is simply ΔCDC - ΔCCC.

If you carry out such a test over the majority of the batteries capacity you'll be able to extrapolate out an accurate estimate of that capacity, see the second image.
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In this graph the slope of the black trendlines of Ah and kWh represent an extrapolation to 1, or in other words to 100% of the battery capacity, advertised at 180 Ah and 64 kWh. The two thin black trendlines are sitting over the blue and red data points so closely you can barely make them out. This also demonstrated that SOC is more closely aligned to change in Ah than kWh. So, range diminishes faster at lower SOC.
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Regarding cell voltage balance I'll note that the car measures this without loading the traction battery, not the case when you're using an OBD2 app. So, it's not entirely accurate but close. Another note is that the cell voltage values have a granularity of 0.02 V and that is almost certainly a truncated value meaning 4.140 could actually be 4.159. The average cell voltage on that app is simply the pack voltage divided by the number of series groups (88) and is much more accurate on a per-cell basis. The Kona cells top out at 4.156 V I think and it seems higher (and risker) than your Ioniq at 4.147.
 

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Very informative posts. I'm an owner of a 28kwh Ioniq for 2 months now and have regularly registered my trips. I like statistics and technical details :) But from my understanding the CEC and CED values are always ~28 kWh no matter what. They seem to be directly related to SoC, whether your battery suffers from degradation or not. Here are a couple of my trips. I documented the consumption displayed by the car, sometimes the CEC & CED values using the ΔCED - 0.98 x ΔCEC formula and also the charged kWh's. My charging losses at home are ~12%. What you see is that the consumption and the charging values match very well (I have a total of ~25,5 kWh available when looking to the 100% - 3% SoC values) but the CEC & CED values are always ~28 kWh.

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First thing, I realised overnight that my water tank analogy was more complicated than the actual battery! As you charge and discharge the battery, coulombs (A x h) aren't lost but a small amount of energy (V x A x h) is lost from voltage drop due to resistance x current. That resistance increases with battery aging. That's all there is to it, at a simple level.

... But from my understanding the CEC and CED values are always ~28 kWh no matter what. They seem to be directly related to SoC, whether your battery suffers from degradation or not.
Yes, pretty much what I see as well, the energy represented by "100% SoC" is always close to the advertised capacity even though my battery is over 3 years old. Plus your data covers a wider range (3-100%) than I can manage, typically 20-90%. Some have suggested in the past that the BMS actively opens up more of the withheld capacity as degradation takes hold. I've never been a fan of that theory because it seems more sophisticated than I expect from an automaker but our experiences do tend to support that this is happening.

I had spent a lot of time analysing the Kona's behaviour initially by dash and charger info but gaining access to BMS data via Torque Pro (plus the data logging) has opened up much more information. But one thing about the OBD data is that the smart people who located those CAN addresses and formatted the output haven't necessarily validated the accuracy or applicability of those values. It's up to us users to ensure that they reflect what we expect. SoH on the Kona with LG cells for example reads 100% for years, while those with SKI cells get a more realistic reading.

Another example is that the realtime pack voltage and current readings are useless when driving but when charging represent charger DC input to the car (including the battery). I've verified that using an ABB 50kW unit which I expect accurately bills by DC energy delivered. Combined with change in CEC you can work out DC charging efficiency, see image below. If you use an external AC power meter you can apply that to AC charging as well and determine OBC efficiency.

Recently I found a discrepancy between dash displayed consumption and net energy via the BMS values. Searching through Hyundai's patents opened up a whole lot of complication that I almost wish I hadn't found. The BMS models the batteries varying and non-linear internal resistance and works out a fake realtime current that when multiplied by the measured instantaneous pack voltage (I assume) more accurately reflects actual effect on SoC change. That fake power value is used for the dash reading and perhaps other things. The fake current is slightly higher than the real current when going up hills for a period of time, or slightly lower when regening for a period of time. While driving on level road or while charging the effect seems to be minimal and zero respectively.
This level of analysis is starting to get over my 'pay grade' as they say and I'm probably not going to try and untangle it, but it's good I know that it's there.
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I probably should have mentioned that the sag in the cumulative energy delivered to the battery under DC charging can only be due to the battery heater kicking in. Ambient (and battery) temp was under 20°C and that must have triggered it. Because it's a "PTC" type of heater it reduces power slowly over a few minutes as it warms up.

If the heater was not present or not needed the lower line would be nearly coincident with the upper line, only differing in slope due to the continuous 0.2 kW it takes to keep the car's electronics alive over what the battery absorbs. Also, with the battery average cycle efficiency being say 98% that means 1% (or even more) of energy entering the pack is emerging as heat and that's why the temperature keeps climbing while the heater itself backs off.

45.9 kW (charger output) = 0.2 kW (car's overheads) + 0.46 kW (1% battery losses) + 45.24 kW (99% charge accepted by battery)
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