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Calculate usable battery capacity based on rated miles values

I got here via the Model S REST API post where I am trying to figure out the values returned from the Tesla API. As the API doesn't return any data about consumption per kilometer or mile I started to do some research.

I have a Tesla Model S100D from 2018 and I'm from the Netherlands. A quick assumption here is that (api) data is the same for all European Tesla's but different from the US models (things like rated miles).

Code:
User interface:
    soc:      55%
    typical: 276km   => 171.49m
    rated:   343m    => 213.13m

Energy display (average):
    10km: 198Wh/km, 271km (168.39km)
    25km: 251Wh/km, 214km (132.97km)
    50km: 261Wh/km, 205km (127.38km)

API: (via Teslafi.com account info)
    battery_level:        55%
    battery_range:       213.21m  => 343.12km (rated in GUI)
    est_battery_range:   127.59m  => 205.33km
    ideal_battery_range: 171.23m  => 168.39km


Based on this data the *only* thing that shows consumption is the energy display estimate. Based on that I've taken that consumption rate (261Wh/km) and converted these to both the battery_range which is *rated* in the European UI and ideal_battery_range.

Code:
Current ranges:
        rated: 342.45km, 212.79m (battery_range)
        ideal: 275.02km, 170.89m
    estimated: 204.93km, 127.34m

Max ranges:
        rated: 622.64km, 386.89m (battery_range)
        ideal: 500.04km, 310.71m
    estimated: 372.61km, 231.53m

Consumption:
        rated: 156.19Wh/km, 251.36Wh/m (battery_range)
        ideal: 194.49Wh/km, 312.99Wh/m
    estimated: 261.00Wh/km, 420.04Wh/m

Pack capacity (SoC: 55%):
      current:  53.49kWh
          max:  97.25kWh

Factors:
    to ideal:     1.24518696237346 (from battery_range)
    to estimated: 1.67103816554107 (from battery_range)

As you can see when extrapolating this to 100% based on the estimate consumption my battery pack has 97.25kWh usable, a rated consumption of 156.19Wh/km and ideal consumption of 194.49Wh/km

Comparing the numbers from the UI and the API and converting from/to miles it means that:

- Typical in the UI is mapped to "ideal_battery_range" in the API
- Rated in the UI is mapped to "battery_range" in the API


Can anyone confirm if these consumption numbers from "rated" and "ideal" are correct?

How do these number compare to the actual CANbus data? That 97kw looks awful familiar as the Usable Battery amount....
 
Has anyone noted a drop in useable capacity lately?

I have a 2013 S85 and Tesla replaced the battery back in Aug 2018. Charged to full it shows 245mi of rated range, but when I go on longer drives and record start/end SOC and kWh consumed, it implies 68-70kWh total usable capacity pretty consistently - I also recently ran it from full all the way to 0% and it only dispatched 69.8kWh.

Anyone else seeing something similar?
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
20,844
30,033
Texas
Has anyone noted a drop in useable capacity lately?

I have a 2013 S85 and Tesla replaced the battery back in Aug 2018. Charged to full it shows 245mi of rated range, but when I go on longer drives and record start/end SOC and kWh consumed, it implies 68-70kWh total usable capacity pretty consistently - I also recently ran it from full all the way to 0% and it only dispatched 69.8kWh.

Anyone else seeing something similar?
I've never ran mine from 100% to zero, so I can't answer that, but around 70-75 kWh usable capacity sounds about right. Getting 285-305 miles on a full charge would be relatively normal in good weather.
 
Has anyone noted a drop in useable capacity lately?

I have a 2013 S85 and Tesla replaced the battery back in Aug 2018. Charged to full it shows 245mi of rated range, but when I go on longer drives and record start/end SOC and kWh consumed, it implies 68-70kWh total usable capacity pretty consistently - I also recently ran it from full all the way to 0% and it only dispatched 69.8kWh.

Anyone else seeing something similar?

Are you able to pull data from the CAN bus? Are the numbers you’re sharing from the instrument cluster?

If you’re showing 245 miles of rated range at 100% displayed SOC, you should have 72.275 kWh which is reported as “Nominal Energy Remaining” via the CAN bus. There’s a 4 kWh energy buffer that appears to be slowly introduced as you get lower in SOC (see this thread for more details), so from 100% displayed SOC to 0% displayed SOC, you should be getting about 68.275 kWh.

Seems normal to me. Even though your battery pack was replaced recently, it might not be brand new. I believe Tesla’s battery warranty states they will replace your pack with the equivalent (or close to) capacity that your original pack had, although I’m sure in some/many cases folks get a brand new one.
 
Has anyone noted a drop in useable capacity lately?

I have a 2013 S85 and Tesla replaced the battery back in Aug 2018. Charged to full it shows 245mi of rated range, but when I go on longer drives and record start/end SOC and kWh consumed, it implies 68-70kWh total usable capacity pretty consistently - I also recently ran it from full all the way to 0% and it only dispatched 69.8kWh.

Anyone else seeing something similar?
So you went from full to 0% and used up 69.8 kWh and 245 rated miles. How many actual miles did you travel in that time?
Any loss in usable capacity will also show up as a loss in rated miles. A new battery for an S85 had about 265 rated miles. How many rated miles did your replacement battery have when you got it in Aug 2018?
Bottom line, your numbers look fine.
 
Are you able to pull data from the CAN bus? Are the numbers you’re sharing from the instrument cluster?

If you’re showing 245 miles of rated range at 100% displayed SOC, you should have 72.275 kWh which is reported as “Nominal Energy Remaining” via the CAN bus. There’s a 4 kWh energy buffer that appears to be slowly introduced as you get lower in SOC (see this thread for more details), so from 100% displayed SOC to 0% displayed SOC, you should be getting about 68.275 kWh.

Seems normal to me. Even though your battery pack was replaced recently, it might not be brand new. I believe Tesla’s battery warranty states they will replace your pack with the equivalent (or close to) capacity that your original pack had, although I’m sure in some/many cases folks get a brand new one.
I would submit that all discussions on battery degradation must contain CANbus data. This whole "my range is xxx @ xx%" or, "I put xx.x amount of electricity in" are useless without out the actual data the car is logging.
 
So you went from full to 0% and used up 69.8 kWh and 245 rated miles. How many actual miles did you travel in that time?
Any loss in usable capacity will also show up as a loss in rated miles. A new battery for an S85 had about 265 rated miles. How many rated miles did your replacement battery have when you got it in Aug 2018?
Bottom line, your numbers look fine.

220mi, 311wh/mi
 
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220mi, 311wh/mi
So adjusted for EPA rated range, you get 231 miles which is 14 miles off of your starting 245 miles which, da-da-da-daaaa, comes out to ~13.5 miles you could have gone if you had used the 4kw below 0%. I think it's pretty clear whats happening. I mean, seriously, is anyone still confused?
 
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I have a Model S 75D that is just over 1.5 years old, about 14K miles. I observe at full, 100% charge about 244 miles rated range. Using the methodology way back in post 1, I get: 244 miles * 0.285 kWH/mile = 69.5 kWH usable capacity. Initial usable capacity according to post 1 was 73.8 kWH for this model, so my degradation appears to be 1- 69.5/73.8 = 5.8% .

a) is this too simplistic ?
b) are other people observing numbers in this range? Perhaps we could crowd-source a degradation curve graph?
 
I have a Model S 75D that is just over 1.5 years old, about 14K miles. I observe at full, 100% charge about 244 miles rated range. Using the methodology way back in post 1, I get: 244 miles * 0.285 kWH/mile = 69.5 kWH usable capacity. Initial usable capacity according to post 1 was 73.8 kWH for this model, so my degradation appears to be 1- 69.5/73.8 = 5.8% .

a) is this too simplistic ?
b) are other people observing numbers in this range? Perhaps we could crowd-source a degradation curve graph?
a) No, it's too complicated. Just do 244/259 (rated miles when new) = 5.8% degradation
b) Yes, you are pretty much like everyone else. There is a composite degradation curve, but to me, the data is so spread out it doesn't really mean much. Sorry I don't have a link to it.
 
It should be more accurate to measure available battery capacity using raw data (SOC and kwh used) than to use a highly derived value like estimated range on a full charge. On my car (2016 S 90D) the rated range on full charge appears to assume that the battery has its nominal capacity and is not degraded. It shows around 285 miles even though my actual range is much less (corrected to 280-290 wh/mi) and my battery has had "exceptional" degradation.
 
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It should be more accurate to measure available battery capacity using raw data (SOC and kwh used) than to use a highly derived value like estimated range on a full charge. On my car (2016 S 90D) the rated range on full charge appears to assume that the battery has its nominal capacity and is not degraded. It shows around 285 miles even though my actual range is much less (corrected to 280-290 wh/mi) and my battery has had "exceptional" degradation.
Not sure why anyone is disagreeing with you. The number on the dash is absolutely meaningless with regards to battery degredation. It's the kw findf in the BMS that count.....
 

ucmndd

Well-Known Member
Mar 10, 2016
10,200
20,050
California
Not sure why anyone is disagreeing with you. The number on the dash is absolutely meaningless with regards to battery degredation. It's the kw findf in the BMS that count.....

The "number on the dash" is calculated directly from the reported capacity of the BMS. Capacity divided by rated wh/mile constant = range in miles. They are one and the same. I'm disagreeing with him (and apparently you) because he's claiming this number is somehow "highly derived" when it's most definitely not. It's simply a different representation of the same data.
 
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Not sure why anyone is disagreeing with you. The number on the dash is absolutely meaningless with regards to battery degredation. It's the kw findf in the BMS that count.....

We discussed this in another thread you were involved in but rated range at 100% SOC appears to be based on the BMS reported value “Nominal Energy Remaining” and EPA rating. The math is exact, so you can use rated range to figure out what your “Nominal Energy Remaining” value is. As you know though, this is only accurate at 100% SOC.

It’s important to note there’s also a BMS reported value called “Nominal Full Pack”. One would think this should be the same as “Nominal Energy Remaining” at 100% SOC but what I’ve found is sometimes it can be 0.1-0.3 kWh less. It seems if you rarely charge to 100%, the charging rate really starts to taper off as you get closer to 100% and you’ll usually see Nominal Energy Remaining is just slightly less than Nominal Full Pack. However, if you charge to 100% more frequently, it will still taper off closer to 100% but not as quickly and you’ll usually see Nominal Energy Remaining = Nominal Full Pack once the charge is complete.

Does any of that matter? Not really, but it’s something to consider if you ever see your rated range change slightly, either up or down. Im fairly certain this is the same reason why some folks see their rated range increase after doing a few discharge/charge cycles. Your battery isn’t magically gaining more capacity, it’s just BMS seems more “confident” in being able to charge all cells to 4.20 volts (aka 100% SOC). Personally, I record Nominal Full Pack (as reported by BMS) and intend to monitor it through the years to get the most accurate picture of how much my battery is degrading. It’s also interesting that at lower SOCs, Nominally Full Pack will often report a slightly lower value (i.e. 75.6 kWh) compared to at higher SOC, it reports a slightly higher value (i.e. 76.2 kWh). So using the method I’m doing, you just have to make sure you’re comparing at similar SOC. Temperature will also obviously affect the reported value (and actual capacity).

Edit: All of this was based on using TM-Spy to read CAN bus data. It wasn’t until after the fact that I learned (by translating the raw CAN frames) TM-Spy displays the BMS reported value “Expected Energy Remaining” which appears to be slightly lower than Nominal Energy Remaining. I’ll have to look at it again the next time I do a 100% SOC, which is rare, but I’m curious how Expected Energy Remaining and Nominal Energy Remaining compare. All that to say, it could be either value that is being used to calculate rated range at 100% SOC (assuming they report the same value at 100% SOC).
 
Last edited:
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The "number on the dash" is calculated directly from the reported capacity of the BMS. Capacity divided by rated wh/mile constant = range in miles. They are one and the same. I'm disagreeing with him (and apparently you) because he's claiming this number is somehow "highly derived" when it's most definitely not. It's simply a different representation of the same data.

It’s probably worth noting this is only true at 100% SOC. Once you get below 100%, displayed rated range appears to start using a value slightly less than Nominal Energy Remaining that ends up being ~4 kWh at 0% SOC or 0 rated miles. In other words, Nominal Energy Remaining reports ~4.0 kWh when displayed SOC is 0%. Turns out, BMS also reports a value called “Energy Buffer” that is 4.0 kWh. Coincidence? Perhaps, but it seems pretty clear to me this energy buffer is gradually accounted for as your SOC decreases as discussed in this thread.
 
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The "number on the dash" is calculated directly from the reported capacity of the BMS. Capacity divided by rated wh/mile constant = range in miles. They are one and the same. I'm disagreeing with him (and apparently you) because he's claiming this number is somehow "highly derived" when it's most definitely not. It's simply a different representation of the same data.
My point is that it's not accurate as to how far you can actually drive because as you approach zero percent, a consumption number other than EPA wpm is used
 
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