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2019 Bolt built June 10th. 66kWh battery?
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Discussion Starter #21 (Edited)
This is the scenario that got me wondering. I drove 185.8 miles (starting at 100%) using 56.2 kWh. The display said I had 34 miles left (minimum 27) with the trip average being 3.3 mi/kWh. The battery level was at 15% - which could in theory be as low as 11% because of how it's displayed. I calculated two different ways - one assuming I would get 3.3 mi/kWh for the remaining 27-34 miles and one where I calculated 56.2 kWh being 85-89% of the battery. Both calculations gave me answers ranging from 63 to 66 kWh pack.
Seems like you may have the larger pack- but you really do need a more accurate estimate of % battery capacity remaining. The MyChevrolet app can give that to you, but I have had inconsistent results trying to use the app with the KeyPass feature, where the battery percent is displayed more exactly.

I use TorquePro to get my exact state of charge- and that gives two different values, one for the display and one for "Raw"! The raw value is a little higher than the displayed value for low states of charge- which give a little greater estimate of capacity, but still within 1 kWh the times that I have noticed it.

Another alternative is to notice exactly when the green bars of the DIC battery indicator blink to the next lower level, and what "kWh Used" shows. I have the home screen on the display customized to show "kWh Used", so it's easy, as long as I remember to look! Using TorquePro and looking at the screen shows that the green bar blinks to the next lowest level at exactly the upper end of the 5% bin. For example it blinks from four to three bars right at 15%.
See also below. It seems that the calculations will be least biased when performed at between 50 and 75% state of charge.
 

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2019 Bolt built June 10th. 66kWh battery?
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Discussion Starter #23 (Edited)
This post is another nerdfest, for sure, but there are a findings and points that everyone thinking about range and battery capacity might be interested in, especially in the last paragraph.

I spent some time and did more careful calculations using data logged by TorquePro for those two long trips in my 2019 Bolt on July 4 and 5th (both about 235 miles on a single charge- 55579 Tom Cat Drive, Homer, to 49th State Brewery in Anchorage, Alaska for those interested in looking on Google or wherever your mapping is happiest). I also added a shorter trip (186 miles), but still using 70% of battery, but with cooler, wetter conditions on July 19th. I wanted to see how Battery % Displayed and Raw State of Charge (SoC) % might vary relative to each other and to kWh Used. That way I could evaluate how accurate the quick-and-dirty method might calculate battery capacity, at least for this small sample size of two trips. If the relationship is strongly non-linear then the calculations will be the most inaccurate over the portions of the curve where the non-linearity is strongest. I found that the quick-and-dirty method seems to be a good one, especially if you can control for other confounding variables such as high and low temperature and aggressive charging and driving history. I encourage you to present other measurements, especially if you have different findings!

Methods
The PIDs that TorquePro collects for the 2019 and later Bolt do not include values for cumulative kWh Used. In MSExcel, I calculated kWh Used using the area under the curve of Time vs Instant kWs of power, both recorded by TorquePro. Averages of adjacent half-second intervals over the duration of the trips were summed and divided by time (1/7200 hour). Another method is to fit a polynomial equation and integrate. However, results from those two methods are probably not significantly different. A shorter time interval would be more accurate, but for a long trip, that's a lot of data for MSExcel!

Wesley (above) mentions that displayed state of charge falls more slowly at high levels compared to kWh used, but falls more rapidly when the state of charge is lower. Wesley mentions that they use an SoC vs kWh Used relationship, but that relationship isn't shown on their graph. I wondered how extreme the non-linear relationship was. Enough to strongly bias calculations of capacity using a quick-and-dirty method described in a previous post? (looking at when the DIC shows 50% or 75% and at the same time noticing the kWh Used display, then doubling or quadrupling, respectively, kWh Used to get an estimate of capacity)

Here's what I got:

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The bottom axis is kWh Used and along the left is the battery percentage. Despite the axis title, two different battery percentages from TorquePro are displayed for each trip, the SoC Raw HD % (darker red, orange and blue) and the Battery % Displayed (lighter red, orange and blue dashes)- the latter is what is used to display the green bars on the Dirver Information center (DIC) on the dashboard. The equations for the linear relationships are also displayed. The coefficients of these equations suggest that overall loss is about 1.5% battery capacity per kWh Used (1.5237% on the 4th, 1.4502% on the 5th, 1.43% on the 19th). It would be interesting to compare these coefficients among trips and different cars. 1/60 kWh = 1.67 and 1/66 kWh = 1.52. Comparison statics could be performed to determine if the coefficients are statistically different at chosen p-values. Those statistics would be a way to objectively demonstrate a significant decline in capacity.

Non-linearity
You can really see the s-shaped relationship that wesley writes about- the values for displayed battery percentage are higher than the raw SoC percentages when the battery is closer to full: the lighter-colored dashed points plot above the darker-colored lines. The lines are very close and nearly perfectly linear about halfway along the curve (between about 50% and 75% SoC). When the battery is closer to empty, the battery display % plots lower than the raw SoC % values. Therefore, especially at high and low states of charge, what's displayed in the car is based on different values than the Raw SoC %. Of course, what's displayed in the car is even coarser because that display is in 5% bins. I did not evaluate how the value for battery % that is displayed in the MyChevrolet app compares to either of these percentages.

The straight dotted lines of the linear relationships show that if the actual relationship between Raw State of Charge % and kWh Used was linear, then the % meter (and Raw SoC) is falling too slowly at first, compared to kWh used, and too quickly at low %, as wesley writes. GM has probably built in a little bit of an extra buffer to help prevent drivers from running out of juice unexpectedly when they are at low battery levels. Good idea!

However, maybe the relationship between Raw SoC % and kWh Used is, in reality, slightly non-linear? If the numbers that TorquePro gathers from the OBDII are accurate and we are interpreting them correctly, then the slight arch in the Raw SoC % vs. kWh Used curves seem to imply that the non-linearity is real. kWh Used declines more slowly at high Raw SoC % and slightly faster at low %.

It seems that a kW should be a kW regardless of the charge status of the battery, but battery capacity is not a fixed number. Since capacity varies depending on many things including temperature and charging history, it seems quite possible that battery capacity could increase ever so slightly when using a nominal kW at 95% SoC, and decrease a little extra when using 1 kW at a 25%. If so, then the quick-and-dirty method is more accurate than either non-linearity would suggest. It appears especially accurate between ~50-75% SoC where depatures from linearity are minor.

Of course, these are just three curves calculated during pretty uniform and benign conditions. I have never used a DC fast charger; there are none in my State. I use a level 2 charger at home to get 32A at 240V. I set my target charge level to 80% unless I'm planning to go on a longer trip. I set the cruise control to the speed limit on longer trips to increase efficiency and make similar trips comparable. At home, I plug in when outside temperatures are below freezing.

Standardize capacity comparisons
These findings suggest that first, get the most accurate % state of charge value at the most specific value for kWh Used that you can. Second, perform the calculation at between 50 and 75% charge where these relationships are the most linear. Using the full range of capacity is next best, because biases at higher states will tend to balance biases at lower states of charge.

Not specific to this analysis: do not perform the calculations when the confounding variables are expected to be especially confounding (high/low air temperatures, lots of fast driving and DC fast-charging to full). This makes god sense. Capacity should be calculated and compared using standardized conditions. If things change, like a DC fast-charger is suddenly installed in a convenient spot and you use it a lot, and the temperature is very much higher or lower, your comparisons won't be that, well, comparable. Measurements like these will always be confounded by degradation. However, Li-ion battery degradation curves suggest that degradation is small; occurring rapidly at first, then very slowly over time. Of course, controlling for conditions is not always possible, so plotting more measurements is better. The outliers should be apparent, especially if concomitant data are collected about relevant conditions.

Discrepancies
The capacity estimates for trips were about 2 kWh below the capacity calculated using "kWh Used" recorded from the car's display (66.17 vs 68.6, 64.3 vs 67.6, and 65.7 vs. 68.5 on the display). This ~2kWh discrepancy is almost certainly because the area-under-the-curve method underestimated the total kWh Used. It calculated that I used 50.8 kWh on the 4th (vs 54.2 on the display), 55.7 on the 5th (vs 56.9 on the display) and 46.3 on the 19th (vs. 48 on the display). Unfortunately for accuracy, on the July 4th trip, TorquePro missed recording about 2 minutes worth of data during the time the battery level was falling below 40%. Even with this missing data and inaccuracy, the area-under-the-curve calculations are probably sufficient to get a good sense of the magnitude and shape of the non-linearity between kWh Used and % States of Charge at any point along the curve.

Factors affecting range/kWh used
The early July trips were pretty similar, but with a few important differences. They were on the same road in dry conditions, but in different directions (a round trip with a stop overnight to charge). Starting elevation on the 4th was 500 feet higher than the ending elevation, so on the 5th there's more of a climb, but there was less weight in the car, maybe 175 pounds. I also had more headwinds on the 5th. The temperature was around 80 degrees F on the 4th and 57 degrees on the 5th. Maybe most importantly, the speed limit increases to 65 mph on a long hill- mostly downhill on the 4th and uphill on the 5th. That is probably the biggest reason that more kWh were used on the 5th, even though the distance was slightly shorter (1.5 miles). Otherwise the speed limit is 55 (mostly) or 45. I set the cruise control to the speed limit on both trips to try to keep conditions as similar as possible, although to make sure I got home on the 5th without charging, I set it to 60 for most of the (uphill) 65 mph zone. I only increased speed to 65 a few times, when a car was behind me without a passing zone.
The July 19th trip was less hilly, cooler- 55 degrees- and rainy. The seat heaters, wipers, and fan were on much of the time. It's flatter and mostly 55 mph the entire way. It was RT from the address above to the Kenai Airport.

I look forward to continued contributions to this subject. Make measurements! Record data!

Addendum:
Another trip (almost identical to the July 19th trip, ~190 miles)- this time I did not record kWh used at the end, so rely solely on the output from TorquePro. I just used calculations from between 25% and 75% because the trip did not begin fully charged. The DIC % fell to 25%, however, SoC Raw did not fall to 25%, thus the missing values. Now I see your point on variability! However, assuming that the "true value" is ~64-66 kWh, it does appear that subtracting the two kWh used values for when when DIC % displays 50% and 75% and multiplying by 4 is reasonably accurate- perhaps the most accurate way to estimate capacity:
30087
 

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2019 Bolt built June 10th. 66kWh battery?
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Discussion Starter #25 (Edited)
It's certainly possible that a battery with zero lost capacity reports more consistently at higher SoC, but that has not been my experience. Even early on, if I only discharged my battery 50% or less, the energy capacity estimates would vary widely. +/- ~5 kWh if memory serves.

You definitely need to cycle the full battery early on just to ensure that you don't have any bad cells, but even just for accurate measurements, you really need to do multiple cycles to account for discrepancies.
See above. If you only discharged to above 50% you would be calculating from values mostly in the more strongly non-linear portion of the curve of SoC % vs. kWh Used, which would give you a more biased result. Based on the preliminary, but robust, analysis above, capacities obtained using values between 75% and 50% SoC should be the least biased, at least during relatively benign conditions. I'd love to see the numbers!
 

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So of those of you MY 2019 owners who think you might have a higher capacity pack, what are your car's build dates?
September, 2018.

There was a guy corresponding with me privately some time ago with similar suspicions. I'll point him at this thread.
 

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September, 2018.

There was a guy corresponding with me privately some time ago with similar suspicions. I'll point him at this thread.
Hmm... That seems rather early to me, but you're right, I know a number of 2019 owners who say their battery capacity is suspiciously high.
 

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The other guy here.

Yes, I have had similar experiences where my car has behaved as if it had more than the rated 60kWh. Due to covid my driving has been greatly reduced, and I have stuck to a charging band of 50-75%, which is not great for any sort of calculation. This thread has renewed my interest though, and I may try for a charge from 100% and see where I end up.

Build date 06/19
 

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2019 Bolt built June 10th. 66kWh battery?
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Discussion Starter #30
Actually, I have been working up a few trips, recorded by TorquePro using OBDII data. I have been plotting SoC against kWh Used and find that the deviation from linearity is least between 50% and 75% SoC. Therefore, the most accurate estimate may be noticing your kWh Used value just as the green charge indicator bar on the dash blinks from 80% to 75%, and again when it blinks from 55 to 50% (not easy!). Subtract those two kWh Used values and multiply by 4 to get an estimate of capacity.
 

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Discussion Starter #31 (Edited)
Two nearly identical trips on different days with clean data from TorquePro:

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The display read 56.9 kWh Used after the trip on the 5th (about 2.1% higher than the calculations based on half-second intervals used in the plot above).
 

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2019 Bolt built June 10th. 66kWh battery?
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Discussion Starter #34 (Edited)
View attachment 30113
No, it is not. kW = V x A

At 399 volts a kW is drawing 2.5 amps from the battery. At 318 volts a kW is drawing 3.1 amps...20% higher amps.
Right-o, I really meant to write that a kWh is the same....But same idea, Thanks for clarifying!
So, it makes sense that at a lower state of charge, in other words a lower voltage, the motor will draw more amps from the battery to to achieve the same power- instantaneaous kWs. This extra draw of power would make the battery capacity look a little lower at low states of charge, and, conversely higher at high states. That explains the arch in the curve of Raw State of Charge vs. kWh Used.
 

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Discussion Starter #35
Cool. Those numbers sure support that hypothesis- at 70% SoC, DIC battery level and raw read the same, and Batt Cap = 57kWh, like you'd expect. Being a 2019, I always get -8.6 kWh for Batt Cap in TorquePro. I am sure glad that my air temperature is always much lower than that!
 
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