[MichBolt]

I will do some napkin math like the WIND-WORKS article to estimate my battery capacity (I've seen a youtuber do this too for calculating battery degradation). In the future, I will try OBD Fusion (no Android for me).

I am guessing that one needs to discharge 16 percentage points or more of battery to get a relatively accurate battery capacity measurement with the napkin math. This value can be found by analyzing the overall behavior of the round off error in the displayed SOC on MyChevrolet (the same can be done for kwh spent value, but if you spend 16%+ of your battery, this value is of less concern!).

16% isn't enough. You need to discharge closer to 75% of the battery because the state of charge curve is not linear. I tracked discharge from 100% down to 15.7% (using ~84% of the battery), and my capacity calculation settled around 64 kWh starting at about 24% SOC (using ~76% of the battery).

If I had only used ~16% of the battery, my capacity calculation could have been 62.4, 65.8, or 63.8 depending on which particular data point I used.

Part of the reason is that the SOC displayed value appears to be "sticky" - it will change in discrete 0.4 kWh increments. Obviously, that can lead to dramatic shifts in your capacity calculation if 16% = 10.2 kWh, 9.8 kWh (10.2-0.4), or 10.6 kWh (10.2+0.4).

 

[enslay]

Part of the reason is that the SOC displayed value appears to be "sticky" - it will change in discrete 0.4 kWh increments. Obviously, that can lead to dramatic shifts in your capacity calculation if 16% = 10.2 kWh, 9.8 kWh (10.2-0.4), or 10.6 kWh (10.2+0.4).

The relative error of 10.2-0.4 and 10.2+0.4 to 10.2 is less than 4%. Not that massive at all.

All of your calculations at 16% SOC difference are within 3% relative error to 64. This is perfectly acceptable accuracy to me and I don't need to run down my battery a whole lot to get this estimate.

EDIT: That isn't to say that I disagree with you. Indeed, if you run down the battery more, your estimate will be even more accurate!

 

[Telek]

16% isn't enough. You need to discharge closer to 75% of the battery because the state of charge curve is not linear. I tracked discharge from 100% down to 15.7% (using ~84% of the battery), and my capacity calculation settled around 64 kWh starting at about 24% SOC (using ~76% of the battery).

If I had only used ~16% of the battery, my capacity calculation could have been 62.4, 65.8, or 63.8 depending on which particular data point I used.

Part of the reason is that the SOC displayed value appears to be "sticky" - it will change in discrete 0.4 kWh increments. Obviously, that can lead to dramatic shifts in your capacity calculation if 16% = 10.2 kWh, 9.8 kWh (10.2-0.4), or 10.6 kWh (10.2+0.4).

Agreed that you need as low as possible, and yeah the resolution of the DIC value is a part of it, but the energy-vs-SOC isn't perfectly linear either across the whole range, and gets a little less near the ends.

But in regards to the resolution, you can "unsticky" them by using the raw SOC relative to the displayed SOC. It takes a bit of spreadsheet-fu but it's possible to automatically recalculate.

For example, just writing something up quickly, this is totally made up, but let's say that you have:

Displayed, RAW

25.6, 27.09
25.2, 27.04 <<<
25.2, 26.99
25.2, 26.94
25.2, 26.88
25.2, 26.83 *** for example, DIC would be 24.99 at this point
25.2, 26.77
25.2, 26.73
25.2, 26.69
24.8, 26.63 <<<

So using the raw when the DIC changes (the <<< lines), which went from 27.04 to 26.63, we can "adjust" the DIC which went from 25.2 to 24.8 over the same period. So the middle line we can calculate that DIC would be 24.99.

You cannot just blanket calculate DIC form RAW, I've tried and it's fuzzy. But you can use the relative differences in RAW between DIC increments to give you additional resolution in the DIC number.

 

[MisterJJ]

FYI, I recently ran from 100% down to 3.896% Raw SoC, 2.353% DIC. Energy used = 62.1. Air temp.: 109 F
Capacity calculation comes out to 64.5 kWh.
PID says 187.54 Ah and 60.01 kWh capacity.

 

[GJETSON]

Capacity calculation comes out to 64.5 kWh.
PID says 187.54 Ah and 60.01 kWh capacity.

!Battery - Pack - Capacity kWh estimated 2019+,Bat Cap Est,2245F9,((A*256)+B)*0.0032,30,70,kWh,7E4

Corrected for your results would be:

!Battery - Pack - Capacity kWh estimated 2019+,Bat Cap Est,2245F9,((A*256)+B)*0.00344,30,70,kWh,7E4

 

[CraigF]

I have a 2021 Bolt with less than 3K miles on it. I've been charging to 75% at home about every other day. This morning, the GOM read 233 miles. I drove 19 miles to work with a 50/50 split of local and hwy miles, never exceeding 65 mph, and I watched the GOM estimate drop rapidly to 191 miles. The temp.'s were at 70s F in the morning and 80s/90s F in the afternoon. My 2017 never behaved like this. Also (and perhaps unrelated), the "Outside Temperature" score on my 2017 used to vary across the entire range of the scale, appropriately. My 2021 will drop below half in the cold, but across temp.'s as high as 100 F, it has never risen above the half-way mark on the scale. I'll check the "Auto Defog" setting based on the advice of an earlier poster in this topic, but I was pretty sure that I disabled that. Any thoughts on either?

 

[MichBolt]

I have a 2021 Bolt with less than 3K miles on it. I've been charging to 75% at home about every other day. This morning, the GOM read 233 miles. I drove 19 miles to work with a 50/50 split of local and hwy miles, never exceeding 65 mph, and I watched the GOM estimate drop rapidly to 191 miles. The temp.'s were at 70s F in the morning and 80s/90s F in the afternoon. My 2017 never behaved like this. Also (and perhaps unrelated), the "Outside Temperature" score on my 2017 used to vary across the entire range of the scale, appropriately. My 2021 will drop below half in the cold, but across temp.'s as high as 100 F, it has never risen above the half-way mark on the scale. I'll check the "Auto Defog" setting based on the advice of an earlier poster in this topic, but I was pretty sure that I disabled that. Any thoughts on either?

Well, if the EPA mileage of a 2021 Bolt is 259 miles, then what would 75% of 259 be? It seems like your "233" is high, and the "191" is actually more accurate. So the GOM appeared to adjust correctly after getting more data (from your driving).