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Super Moderator
2020 Chevrolet Bolt
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Cool post! Thanks.

It must not be linear. I get an average of 4 miles/kwh and my 87% charge range is ~207 miles in my new 2021 Bolt. About 2-3 weeks ago, it used to predict ~225 at 87%. And when I bought it a month ago, it was ~259 at full charge. My current 87% range seems low but I guess it's the GOM. I will play with OBD2 to see if a cell went bad or something... but I'm guessing it's not linear (i.e. it's not simply 259*0.87 for SOC and rated milage nor is it simply 4*65*0.87 for average miles/kwh, 65kwh battery and SOC, etc...).

However, I do a lot of 70+ mph highway driving. My 4 miles/kwh comes from going downhill to work one way and uphill the other... all the while going 70+ mph mostly both ways. It somehow averages out to 4 miles/kwh though!
That makes me wonder if speed is weighted more heavily than terrain in the GOM algorithm. It may not be a direct calculation based on overall miles / kWh efficiency.

Also, is your auto-defog setting turned on or off? As the weather gets warmer or more humid, auto defog may run more and impact your GOM. I've noticed that simply turning on the A/C or heater will immediately affect my GOM, regardless of my miles / kWh efficiency at the time.
 

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Super Moderator
2020 Chevrolet Bolt
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2,681 Posts
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).
 

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Super Moderator
2020 Chevrolet Bolt
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2,681 Posts
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).
 

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Super Moderator
2020 Chevrolet Bolt
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Hmm, I had a different situation happen.

A few days ago, and after backing out of my parking space, and dropping the selector into D, my main range dropped 20 miles. But, the next day, when I turned it on, the 20 miles were regained.

Now, this morning, the same thing happened, except it dropped 10 miles.

Has anyone else had something like this happen?
Auto defog setting? Auto defog can run the A/C or heat without any visual indicator, and running A/C or heat will immediately reduce the GOM estimate.
 

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Super Moderator
2020 Chevrolet Bolt
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Hmm, I don't think so, as the weather hasn't warranted this. But, I'll check it out.

However, what would account the the miles being added back the next AM?
Auto defog uses the A/C and heat to regulate the humidity in the passenger space. It can turn either or both on or off at almost any temperature. If it turns off in the morning, your GOM will be higher. If it turns on as you start pulling out of your parking space, your GOM will be lower.

At least it's one variable to remove from the equation.
 
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