Calculate usable battery capacity based on rated miles values

[boonedocks]

4 drives of varying length in widely varying temperature, from the perspective of "maybe the trip meter is right":

Trip meter reported kWh / change in reported SoC = kWh estimated usable

62.1/(.93-.12) = 76.67
53.8/(1-.28) = 74.72
21.32/(.69-.41) = 76.14
48.6/(.89-.25) = 75.94

Seems terribly consistent, even using nearly all of pack capacity. That's a nice 75kWh pack I have there.

Sure enough considering WK057 reported that (my old car) the 85kWh battery only has ~77.5 kWh usable.

This is QUITE the nice 75kWh pack you have there!!

 

[AWDtsla]

Sure enough considering WK057 reported that (my old car) the 85kWh battery only has ~77.5 kWh usable.

This is QUITE the nice 75kWh pack you have there!!

To add insult to injury, Tesla calls mine a 90.

 

[DB 2]

At the risk of being yelled at, I think the problem comes from assuming that 0 miles remaining equals 0 kWh remaining. I know for a fact that a SW limited 60 still has about 3.8 kWh remaining at 0 miles (from the BMS). Until proven otherwise, I say something similar is true for non-SW limited cars. It would explain the reported discrepancy between Wh per rated mile observed when driving and Wh per rated mile calculated from @wk057's kWh pack capacity.

 

[wdolson]

With a non-SW limited car when you reach 0 rated miles, you're into a twilight zone where continuing to draw energy can harm the battery (li-ion batteries don't like to be completely drained) and the car can't really predict when the car is not going to have enough energy left in the battery to keep the car moving.

I have seen some people report getting a number of miles after the car said 0 rated miles and others who have said the car was dead by the side of the road almost immediately after reaching 0.

 

[Dan43]

Someone UK based mis-judged their trip and was quite shy of their SC site when 0 was arrived at, they travelled for 8 more miles and made it to the SC site so they say.
Not sure I am that brave but have been down to 0 miles a few times, on purpose, to charge back to 100% but I can't imagine trying the above mind.

 

[ran349]

At the risk of being yelled at, I think the problem comes from assuming that 0 miles remaining equals 0 kWh remaining. I know for a fact that a SW limited 60 still has about 3.8 kWh remaining at 0 miles (from the BMS). Until proven otherwise, I say something similar is true for non-SW limited cars. It would explain the reported discrepancy between Wh per rated mile observed when driving and Wh per rated mile calculated from @wk057's kWh pack capacity.

So you had 3.8 kWh remaining at 0 miles. How many kWh and rated miles did you have at 100% charge in that case? Trying to figure your Wh/rated miles in that scenario. What I wonder is if the 3.8 kWh includes the anti-bricking buffer. If the anti-bricking buffer is 2.4 kWh, then you only had a few more miles to go before you were going to run out. I think that is what you would expect.

 

[DB 2]

So you had 3.8 kWh remaining at 0 miles. How many kWh and rated miles did you have at 100% charge in that case? Trying to figure your Wh/rated miles in that scenario. What I wonder is if the 3.8 kWh includes the anti-bricking buffer. If the anti-bricking buffer is 2.4 kWh, then you only had a few more miles to go before you were going to run out. I think that is what you would expect.

The anti-bricking buffer is not included in the BMS reported pack capacity or remaining charge. At this time at 100% I get 203 rated miles. As far as kWh I have 60.5 at 100%, but that includes the 3.8 kWh below the zero point. Therefore, I have 56.7 kWh from 100% to 0% (on the dashboard) and 3.8 kWh from 0% to true zero (BMS zero). These figures yield a charging Wh/rated mile of 298 (very close to @wk057's 295), but a driving Wh/rated mile of 279, which is the same as what I see on the trip odometer's power consumption meter on long, single-leg drives. Here are a couple of montage photos/screenshots to illustrate:

This is just after the icon changed from 1 mile to 0 miles. I reset Trip A. On the right is BMS data from TM-Spy showing 3.8 of 70.5 kWh remaining. The BMS reports on the full pack and may be unaware it is in a SW limited car. (When fully charged, the SOC= shows 86.0% just as @wk057 reported)

This is after driving for 17 more miles and using 4.0 kWh. Now the BMS says I am empty. Good time to put the car in the garage and feed the poor, starving beast. Notice on the lower left the graph from the touchscreen Energy app. The icon on the left shows 0% but is plotted at about -6.3%. The icon on the right correctly shows -8%.

 

[henderrj]

First, a bit of a warning to those easily offended by anything negative about Tesla: I've posted several threads about the actual capacities of Tesla battery packs. Raw data with mixed reception. Unfortunately it seems like any time anyone posts a thread that puts Tesla in a negative light most of them tend to get overrun by posts that either aren't on topic or try incessantly to defend Tesla's failing. Bluntly, this thread is not the place for defending Tesla, explaining why they chose to operate as they do, etc. This is about the raw data. Let's gather it, share it, and discuss it logically. If you don't like the data, honestly I don't care. Facts are facts. I don't care if they don't "matter" to you or if you think they don't "matter" to others, and frankly I don't think anyone else cares either. Again, this is about discussing the data and the numbers. Not about how you feel about them. Anyway, sorry about that. The above is my best effort to not have this thread overtaken by nonsense. It's certain to fail, but worth a shot I suppose.

To the facts.

In a previous thread I posted this data about actual pack capacities after gathering data from multiple cars of each variety:


As it turns out, at or near 100% displayed charge the rated miles (not ideal) * the static rated miles value for the vehicle type/config matches the BMS's reported total usable capacity to within about +/- 1 kWh in nearly all cases I've checked on real cars. The disparity is mainly due to lack of significant figures beyond rated miles, the fact that Tesla rounded the rated miles number to a nearest 5 Wh, and the fact that the car seems to round up on reported rated miles. Also, the rated miles display is not refreshed constantly when the BMS value changes, so there is some latency there. Extrapolating from SoC under 100% results in numbers that are very close, but tend to be off due to other factors.

In general, what you need to calculate capacity are the exact static rated mile values for your type of configuration. And actually, they're pretty simple. Here they are:

• All RWD Cars (non-Performance and Performance): 295 Wh/Rated Mile
• All Pre-refresh Model S Dual Motor, non-Performance: 290 Wh/Rated Mile
• Refresh Model S Dual Motor, non-Performance under 100 kWh: 285 Wh/Rated Mile
• Model X Dual Motor, non-Performance under 100 kWh: 320 Wh/Rated Mile
• Model S Dual Motor, Performance under 100 kWh: 310 Wh/Rated Mile
• Model X Dual Motor, Performance under 100 kWh: 333 Wh/Rated Mile
• Model X Dual Motor, Performance 100 kWh: 342 Wh/Rated Mile

Quick notes: Rated miles are EPA miles. I'm unsure what systems are used in other parts of the world. Internally on the cars everything in miles and uses these numbers then calculates the values for other regions using these as a base.

These are the exact numbers pulled from the Tesla firmware. Rated miles are static Wh/mi. They do not change with driving style or anything else besides the configuration of the car as noted above. The car simply takes the estimated usable energy remaining as reported by the BMS, divides by the appropriate static number above, and displays the value. There is another static value for "ideal" miles, but I haven't bothered to gather it.

For example, at my last 100% charge on my X P90D I reached 245 rated miles. To get kWh usable I look at the list above, pick 333 Wh/Rated mile because it matches my car. Then, I take 245 * 333 to get Wh usable. Then divide by 1000 to get kWh. In this example, I end up with 81.6 kWh usable capacity. The BMS on this car reports 81.7 kWh full usable capacity, so pretty darn close.

For fun, lets use the EPA range numbers from Tesla's website for some examples. All for sale now are refreshed versions, so keep that in mind.

• Model S 60 (s/w limited 75): 210 rated miles * 295 Wh/mi = ~62 kWh usable
• Model S 75: 249 rated miles * 295 Wh/mi = ~73.5 kWh usable
• Model S 60D (s/w limited 75): 218 rated miles * 285 Wh/mi = ~62.1 kWh usable
• Model S 75D: 259 rated miles * 285 Wh/mi = ~73.8 kWh usable
• Model S 90D: 294 rates miles * 285 Wh/mi = ~83.8 kWh usable
• Model S P100D: 315 rated miles * 314 Wh/mi = ~98.9 kWh usable (* Estimated Wh/mi)
• Model X 75D: 237 rated miles * 320 Wh/mi = ~75.8 kWh usable
• Model X 90D: 257 rated miles * 320 Wh/mi = ~82.2 kWh usable
• Model X P100D: 289 rated miles * 342 Wh/mi = ~98.8 kWh usable

As you can see, these numbers actually pretty closely match the capacity values I posted previously. The refresh S 90D appears to make the capacity appear to be a little overrated vs actual capacity, and the X 75D seems to really overstate usable capacity. by over 3 kWh... I'm unsure the reasoning for this. Keep in mind that the rated miles Wh numbers Tesla uses are always rounded to the nearest 5 Wh... which over ~300 miles of rated range is a potential disparity of about +/- 750 Wh before accounting for other factors.

A fun extrapolation: A Model S 100D would have a rated range of 337 miles.

It's also pretty interesting that given the internal static rated miles values the range numbers on Tesla's website pretty closely match actual usable capacity values. However, if you tried to go by the advertised capacity values (60,75,85,90,100, etc) to come up with a rated miles value you'd end up with something totally different in all cases. After taking the 4 or 2.4 kWh unusable portion into account (for the 85,90,100 or 60,70,75 packs respectively), the only cars still sold where advertised capacity doesn't match actual total capacity appears to be the 90. Previous 85 variants would also fall into this category as well. The 60, 75, and 100 actually appear to have packs of at least their advertised total capacities after taking the unusable portions into account. (Only opinion based portion of this post: On that note, perhaps Tesla is trying to actually match their name plate/advertised capacities on newer car variants. Doesn't really help people who own "85"s and "90"s that are short several kWh vs advertised, but, it's a start.)

Anyway, mainly wanted to put out the internal rated miles values so that people can calculate their actual available usable capacities. Should be interesting to see data from more than just the cars I've looked at.

-wk

Edit: Updated some data for 100 kWh variants.

I'll contribute my thanks to you also Jason. I bought a used December 2014 85 rear wheel drive and a according to your figures my 260 miles 100% charge I'm at 98.97% capacity. I think the numbers actually make Tesla look good! Certainly it's encouraging.

 

[bp1000]

Does anyone know the wh/mile constants for each model for Europe, used in the typical (rated) range calculation?

I've read the p85d is 320 wh/mile in Europe vs 300 in US

I wondered about the other models too.

 

[Dan43]

The anti-bricking buffer is not included in the BMS reported pack capacity or remaining charge. At this time at 100% I get 203 rated miles. As far as kWh I have 60.5 at 100%, but that includes the 3.8 kWh below the zero point. Therefore, I have 56.7 kWh from 100% to 0% (on the dashboard) and 3.8 kWh from 0% to true zero (BMS zero). These figures yield a charging Wh/rated mile of 298 (very close to @wk057's 295), but a driving Wh/rated mile of 279, which is the same as what I see on the trip odometer's power consumption meter on long, single-leg drives. Here are a couple of montage photos/screenshots to illustrate:

View attachment 222498

This is just after the icon changed from 1 mile to 0 miles. I reset Trip A. On the right is BMS data from TM-Spy showing 3.8 of 70.5 kWh remaining. The BMS reports on the full pack and may be unaware it is in a SW limited car. (When fully charged, the SOC= shows 86.0% just as @wk057 reported)


View attachment 222501


This is after driving for 17 more miles and using 4.0 kWh. Now the BMS says I am empty. Good time to put the car in the garage and feed the poor, starving beast. Notice on the lower left the graph from the touchscreen Energy app. The icon on the left shows 0% but is plotted at about -6.3%. The icon on the right correctly shows -8%.

Just caught this, great info.

If then the BMS plots accurately that you have driven another 17 miles for 4kWh usage, when you charged back to say 100% would you of had an extra 17miles added to your total available or does it default to the 0% being equal to the 4kWh you used.

Intrigued to know if you got an extra 17 miles from the battery to actually use (without relying on the BMS calculations all the time)

 

[DB 2]

If then the BMS plots accurately that you have driven another 17 miles for 4kWh usage, when you charged back to say 100% would you of had an extra 17miles added to your total available or does it default to the 0% being equal to the 4kWh you used.

Intrigued to know if you got an extra 17 miles from the battery to actually use (without relying on the BMS calculations all the time)

You do not "expose" the below zero capacity in the UI simply by proving that it exists. Your rated miles available after a full charge will be more or less the same as it was before the below zero excursion. When you start to charge from true zero, the UI reported charging data does not begin to increment until after the below zero capacity has been replenished. This is true for both the miles added during the charging session and the kWh added during the session. This deception (particularly the kWh counter) is necessary to keep the Wh per rated mile consistent while still keeping the below zero capacity hidden. The only way I'm aware of to estimate remaining capacity once you are below zero is by how severely available power is being restricted, which is displayed by the yellow dotted line at the top of the power gauge on the instrument cluster. (or by monitoring the BMS of course)

 

[Dan43]

You do not "expose" the below zero capacity in the UI simply by proving that it exists. Your rated miles available after a full charge will be more or less the same as it was before the below zero excursion. When you start to charge from true zero, the UI reported charging data does not begin to increment until after the below zero capacity has been replenished. This is true for both the miles added during the charging session and the kWh added during the session. This deception (particularly the kWh counter) is necessary to keep the Wh per rated mile consistent while still keeping the below zero capacity hidden. The only way I'm aware of to estimate remaining capacity once you are below zero is by how severely available power is being restricted, which is displayed by the yellow dotted line at the top of the power gauge on the instrument cluster. (or by monitoring the BMS of course)

Thanks.

I wasn't sure if a new zero was created to measure from, but as explained it just stays where it is.

Not sure I am ready to run the car via the BMS to squeeze a few extra miles out at reduced power either.

Thanks for a well explained reply.

 

[Dan43]

Just one more question, does the fact you drive under the 0 miles as set by the car, if calibrating your battery to reset the BMS software measurements of what you have in the battery, and perhaps squeeze a couple or more miles for that re-calibration, does driving to -8% (I have seen on a UK thread a -17% was mentioned and they conceded the car then stopped and needed towing) help that overall re-calibration?

 

[hiroshiy]

Does anyone know the wh/mile constants for each model for Europe, used in the typical (rated) range calculation?

I've read the p85d is 320 wh/mile in Europe vs 300 in US

I wondered about the other models too.

@bp1000 , I have a similar question.

Japanese cars seems to have the same constants as the European cars, with 320Wh/m for typical (rated) range for older single motor models. However newer dual motor models seems to have 290Wh/m, same as American cars.

As an another data point, @wk057 showed that X P100D has 342Wh/m or 214Wh/km but my car shows about 229Wh/km or 368Wh/m from the Energy Graph.

 

[DB 2]

Just one more question, does the fact you drive under the 0 miles as set by the car, if calibrating your battery to reset the BMS software measurements of what you have in the battery, and perhaps squeeze a couple or more miles for that re-calibration, does driving to -8% (I have seen on a UK thread a -17% was mentioned and they conceded the car then stopped and needed towing) help that overall re-calibration?

First, I highly doubt -17% would be achievable. Even the -8% in my post assumed I could drive 5 more miles, which I doubt. I was at about -6.3% when I decided it was time to quit and put the car on the charger. Regarding your question about calibration of the BMS, theoretically it should be a little more accurate, but I have not seen anything that makes me think it is significantly more accurate than simply driving to near zero on the UI and charging to near full. I don't think it is necessary to take it to extremes in either direction to get the BMS more or less as accurate as possible. However, my hunch is that if you never take it out of the 20% to 80% range, then the BMS could get materially inaccurate. This might be at least part of the explanation for the reports of shutdowns while the UI still showed a few miles remaining (along with high speeds, hills and cold, etc.)

 

[electric frank]

As a complete EV (except GEM cars) newbie awaiting delivery of my 2014 CPO S85, I find all this increasingly intimidating. Can't one just rely on the car to digest your driving patterns,current power drain,and display the miles left in your tank? Does it make a difference in your planning if your range is 200 vs 215 miles? I would think in a very short span one would understand their wh/mi within a range and just live within that parameter??

 

[gregd]

As a complete EV (except GEM cars) newbie awaiting delivery of my 2014 CPO S85, I find all this increasingly intimidating. Can't one just rely on the car to digest your driving patterns,current power drain,and display the miles left in your tank? Does it make a difference in your planning if your range is 200 vs 215 miles? I would think in a very short span one would understand their wh/mi within a range and just live within that parameter??

No, in practice, it doesn't really matter much. Sometimes we are our worst enemies. We're all obsessed about the details here, trying to understand how it all works. But in the ICEs of the past we had absolutely no clue what their remaining range was, and gas gauges that were blunt instruments at best. I had one car that would read significantly different after left or right turns. {shrug} You figure it out pretty quickly.

A Tesla has about the same range as most of the ICEs of the past, and offers considerably more advanced instrumentation to help guide you to charging along your trips, as needed. Be a little conservative when you get the car (and congrats!), until you get the feel of it. Most of the stuff that affects range applies to all cars; we just get to see it more clearly due to the instrumentation.

 

[ohmman]

As a complete EV (except GEM cars) newbie awaiting delivery of my 2014 CPO S85, I find all this increasingly intimidating. Can't one just rely on the car to digest your driving patterns,current power drain,and display the miles left in your tank? Does it make a difference in your planning if your range is 200 vs 215 miles? I would think in a very short span one would understand their wh/mi within a range and just live within that parameter??

You're reading a techie thread about some relative minutiae regarding battery degradation. As @gregd put it above, this is more for geeking out than anything else.

The car tells you what range you have left, and it's relatively accurate. You'll find it quite simple to digest. No worries! And congrats.

 

[MarcG]

You're reading a techie thread about some relative minutiae regarding battery degradation. As @gregd put it above, this is more for geeking out than anything else.

The car tells you what range you have left, and it's relatively accurate. You'll find it quite simple to digest. No worries! And congrats.

+1

And just in case you didn't know, the range remaining that is shown in the instrument cluster is the EPA-based number - not based on your driving habits.

If you want to see your estimated remaining range based on how you drove the last 5, 15, or 30 miles, just open the energy app on the center display and select the Comsumption tab. This will show you the projected range (select average, not instant) which is calculated for the last 5, 15, or 30 miles depending on your driving habit.

Hope this helps!

PS: here's an extreme example after going down a steep mountain for a long time:

 

[electric frank]

You're reading a techie thread about some relative minutiae regarding battery degradation. As @gregd put it above, this is more for geeking out than anything else.

The car tells you what range you have left, and it's relatively accurate. You'll find it quite simple to digest. No worries! And congrats.

Thanks, ohmman. I picked up the car 4 days ago and am quickly realizing I'm a bigger fan of the KISS & JFDI (just friggin drive it) operating methodologys than I would have thought !