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Question regarding EPA rated "range", consumption numbers and testing methodology

Discussion in 'Model S: Battery & Charging' started by jeffnorman, Sep 4, 2013.

  1. jeffnorman

    jeffnorman Member

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    According to the EPA, the Tesla S is rated for 265 miles range (85Kwh battery).

    However, the same EPA sticker info says that Model S consumes 38 KwH/100 miles of driving (average city and highway), which seems high but is obviously based on some testing methodology that must build in AC usage, wind, etc.

    At 38 Kwh/100 miles, my 85Kwh battery would give me only 223.7 miles of rated range, so the "EPA Rated 265 mile range" must come from some other consumption data/method. Can anyone shed light on this? I am only interested in how the EPA came up with the 265 mile range number; I realize that the 38 Khw/100 miles number is far above most folks average usage.

    I did find this link to a detailed excel file: http://www.fueleconomy.gov/feg/epadata/12data.zip . However, I could not find any energy consumption numbers that match up to the 265 rated range. Further, that data file raises another question: according to the EPA data file, the battery is 350 volts and has a capacity of 237 amp-hours. That would seem to equate to 82.95 Kwh of capacity. Not to be nitpicky, but 82.95 Kwh is less than the advertised 85Kwh (and charging an extra 2 Kwh at an RV park at 30 amps takes 20-30 minutes so not inconsequential). It could be that there is a 2Kwh reserve, but that would seem inconsistent with the conclusion reached in other threads that the rated mileage/consumption includes the reserve. Or is it just that "P85" sounded better than "P83"?

    Also, does anyone have a link to the actual report where the testing of the Model S specifically is detailed? I am interested in how the EPA measured the consumption and range (e..g, did they run it on a dynometer until the battery was bricked? rely on the Model S onboard energy reporting app? use some other direct measurement of battery consumption?)
     
  2. mknox

    mknox Well-Known Member

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    I believe the 265 miles is how far you can go once the battery is fully charged.

    The Wh/mi number comes from what it takes to get that battery fully charged, and includes things like charger inefficiencies (losses) and perhaps even some of the power needed to "condition" (i.e. heat or cool) the battery as it's charged.
     
  3. jeffnorman

    jeffnorman Member

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    Well, maybe. The EPA has an unadjusted number too - 30.2 Kw/100 miles. The unadjusted number is supposed to reflect driving without any such losses (ac off, no wind, etc.) on a dynometer. However, at 30.2 Kw/100 miles the 82.95 Kwh battery should yield an "unadjusted" rating of 274.67 rated miles. Using the "adjusted" 38 kw/100 miles to account for such losses, the 82.95 kwh battery would yield 218.3 miles of rated range. So I can see how you would get 274.67 "unadjusted" rated miles, and I can see how you would get 218.3 "adjusted" rated miles. But how do you get to 265?! Note that if you use 85Kwh for the battery you get higher numbers, but still no answer to the 265 number.
     
  4. mknox

    mknox Well-Known Member

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    The charging losses I was referring to are associated with putting power into the car's battery. The losses you're referring to above are associated with taking power out of the car's battery, and I think this is where the difference might be.

    Once you have the car's battery full, you can test and rate it with no accessories (lights, heat etc. off) and no wind, and then you can rate it with typical accessories and headwinds.

    On the other side of the coin, you have to get power into the battery in the first place and it will take more than, say, 85 kWh from the wall to end up with 85 kWh in the battery. This is because there are losses associated with charging the battery. Some power is lost to heat (charger inefficiencies) as well as to some of the ancillary components from the pack heater/cooler to the flashing green chargeport light. All of these things take power from the wall that doesn't end up in the battery.
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    I addressed this a while back in a post:
    http://www.teslamotorsclub.com/showthread.php/8252-EPA-range/page2?p=131711&viewfull=1#post131711

    Long story short, the EPA efficiency number measures the AC electricity used to charge the car. So you can't use the 85kWh nominal battery capacity to figure out the range with the efficiency number. You can however figure out how much electricity was used to charge the car (38kWh/100mi * 265 mi = 100.7kWh).

    I would not put too much stock in the battery capacity numbers. If you look further down, it also says the RAV4 EV has 50.18kWh (386V*130) which is unlikely.
     
  6. bluetinc

    bluetinc Member

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    Hey Jeff,

    Where did you find the 30.2kWh/100 mi from? That is very interesting because that is exactly the "rated mile" energy unit (302 Wh/mi) that I have found in all newer 85kWh cars, while my older car is a little different. I am very interested in I could dig up an older one that shows the same number as my car (~306.5Wh/mi)...

    When my car was new, it did show ~275 miles or "rated" range, which matches your unadjusted number below. I would also really like the hear the testing methodology behind this testing also. My best guess would be that they didn't want to use a battery pack that was about to immediately degrade from ~275 miles of range to ~265 miles of range, so they picked something like 10k miles and used the numbers for the expected pack size/range from that.

    I'm also very interested in knowing if that 265 miles of range was tested right up until the car showed a "Car Shutting Down" popup and stopped moving...


    As a side thought to your 82.95kWh battery size question. Are we buying a car that has a perticular size battery, or one that travels a particular distance. If Tesla transitioned a more efficient inverter/motor/Cd, and was able to provide the said 265 miles of range from a 70kWh battery (16%), would they have to say anything? What about a 1.5% change?


    Peter



     
  7. jeffnorman

    jeffnorman Member

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    #7 jeffnorman, Sep 4, 2013
    Last edited: Sep 4, 2013
    In the spreadsheet I linked to above (from the EPA), go to the EV tab, and look at row 10 (row 9 is gasoline equivalent; row 10 is in 100 wh/mile format so more useful for us), and look at columns M, N and O - these are the "unadjusted" consumption numbers (in 100 wh/mile increments).

    These numbers are based on actual testing on a dyno (according to EPA anyway). The testing is done in the EPA lab by the manufacturer under the "supervision" of EPA. These tests are relatively short (measured in seconds) so I doubt that Tesla was worried about degradation. The "rated range" is supposed to reflect a "real world" range in mixed highway/city driving (different from the efficiency numbers which measure range as a function of AC input). I just don't get how they came up with 265 based on the unadjusted and/or adjusted rated ranges from testing.

    I guess that, ideally, I would like to buy a car that has BOTH a minimum size (in KwH or similar capacity measure) AND a minimum range per KwH. Or better, the size in KwH * range per KwH should be maintained at as a minimum (so a 50% increase in efficiency could translate into a 50% smaller battery all other factors being equal and I would be equally happy).

    I am very happy with 30.2 watts/100 miles from the EPA unadjusted figures, as that reflects my own highway driving even when using AC in hot weather. What I am disappointed with is that the battery does not seem to have 265 miles in it even if I drive consistently at 30.2 watts/100 miles!! Emulating the exact consumption pattern from the EPA test (30.2 watts/100 miles) SHOULD give me at least the rated range, but it doesn't (the subject of the Energy Accounting thread). This so far is my only disappointment - I feel that Tesla is misleading the public on rated range. IF the rated range of 265 is there, but "hidden" by a magical Troll that takes away rated miles as we drive so as to create a secret reserve, Tesla should come clean about what it is doing and should provide drivers tools to allow a driver to hit the full rated range even while dipping into the reserve.

    In other words, I should be able to SAFELY and with confidence drive at least 265 miles on a full max range charge if I maintain the overall average of 30.2 watts/100 miles for the entire trip. In practice, however, it is impossible to go 265 miles at 30.2 watts/100 miles without going into the zone of "zero" rated miles for the last 15-20 miles. Why? Because Tesla thought it better to hide the reserve while at the same time advertising 265 rated miles? That is pretty disappointing if so (and I stress IF so, because I am still very skeptical that this explaction is correct). And if I ignore the zero rated miles warning and continue to the full 265 miles? That is especially stressful when the consequences of being wrong are a ruined battery and a long delay to tow my car to the nearest Tesla service center for a $12,000 repair (and would Tesla honor the battery warranty in that case?). So calling rated range 265 seems like a fraud to me unless Telsa is willing to come out and say that you can safely drive 265 miles and disregard the warnings (so long as you maintain the 30.2 or better watts/100 miles average).

    EDIT: Even if my car as a "P83" and "only" had a rated range of 249 miles at 304 watts/200 miles (which seems to jive better with actual numbers displayed on the speedo), it would still be by far the best EV out there. So what is troubling me is why Tesla would be misleading with the rated range numbers (or, instead, whether there is some deeper problem like battery variability or non-consumption losses that we have yet to discover). I think it would be very instructive to know exactly how the EPA tested for this reason alone.
     
  8. vgrinshpun

    vgrinshpun Active Member

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    The following detailed explanation is from Tesla Model S Delivery Checklist and Buyers/Owners Guide prepared by nickjhowe on TM and TMC:

    So how far can I really drive?


    Rod and Barbara on the TM forum in this thread have finally got to the bottom of the battery/range situation in the 85kWh car. Here’s what they found. It is a bit weird, so stick with it:
    The battery is 85kWh
    Usable capacity is only 81.1kWh - the other 3.9 is restricted to system use to avoid ‘bricking’ the battery. This capacity is never available for driving
    The EPA 265 mile range is based on this 81.1kWh capacity
    When the range reads ‘zero miles’ there is actually about 17 miles left (to get you somewhere safe in an emergency); the EPA 265 miles includes these 17 miles.
    265 miles from 81.1 kWh is 306 Wh/mile. This figure has been known for a long time and is what we’ve been using to calculate ‘rated range’.
    BUT - turns out this is wrong. The 17 mile emergency reserve means there are 5.2 kWh held in reserve (but available). When ‘fully charged’ on a range charge the display shows 265 rated miles, but the display drops to zero when there is still 17 miles of capacity. Therefore the ‘rated range’ in the car is based on 265 miles from 75.9 kWh (81.1-5.2), therefore 286 Wh/m.
    So, if you want to get your real range to match rated range as displayed in the car, you need to average 287 Wh/m. But when you get to zero, you’ve still got 17 miles at 306 Wh/m (or just over 18 at 287)
    The net-net from this is that the usable capacity of an 85kWh battery during range-charge, non-emergency driving is 75.9 kWh, and 67.4 kWh for a normal charge. So if you divide that by your Wh/m consumption you should get an accurate estimation of range. I’ve got a lifetime average 340 Wh/m so I would get 223 miles from a range charge. YMMV.


    Note: Much of this information has not been officially confirmed by Tesla and may be wrong, but does agree with everything many users have seen in the last few months. The 15-17 mile ‘reserve’ was confirmed during the infamous “Broder incident.”

    The full document linked below:
    Model S Delivery Checklist and Owners Guide
     
  9. stopcrazypp

    stopcrazypp Well-Known Member

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    #9 stopcrazypp, Sep 4, 2013
    Last edited: Sep 4, 2013
    I take it this is has an exact analogy with a low fuel light in conventional cars. When you reach "empty" you aren't really empty. It's there to discourage people from trying to drive down to the last drop (or Wh in this case) because there are negative impacts to this (Model S would need a tow, ICE car might have a damaged fuel pump and debris from the bottom of the tank sucked into the engine).

    The EPA tests until the car can't maintain the pace of the given cycle. What the dash says in terms of range left is irrelevant to this (it's empirical testing, while what the dash says is a guesstimate with any number of adjustments).
    Read the link I gave in my previous post and the supporting links. This specific PDF explains the test procedure in detail:
    http://www.smidgeindustriesltd.com/leaf/EPA/EPA_test_procedure_for_EVs-PHEVs-1-13-2011.pdf

    I guess your issue with the battery number is like the 16/32/64GB numbers given to tablets. Not all of it is available to the user. In the Model S case, it's unclear what the 85kWh number entails in terms of usable capacity (reserve included). I'm certainly interested in finding out (would help in the investors thread to come up with an accurate battery model for the Model S). We do know the Leaf's 24kWh only means 21kWh usable.
     
  10. jeffnorman

    jeffnorman Member

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    I don't have a problem with Tesla keeping an emergency reserve hidden so long as it starts and remains hidden. Like investors, distance driving in an EV absolutely requires predictability, especially when you are in the midwest where there is only one supercharger within in the entire 12 state area! It isn't like that on the coasts - the rest of us have to deal with J1772 charging and campground charging when traveling (for now). In an ICE vehicle, if I run that tank down past empty and run out of gas, any time and anywhere I can call AAA (or Onstar, etc.) and will have a few gallons of gas delivered with very little delay. Here in the hinterland (at least as it appears from the supercharger map), what can I do if I run out of charge!?? Predictability and *knowing* the absolute remaining range is critical if I am to continue using the Tesla as my only vehicle and for longer drives (which is the case as I sold my AMG to justify the Tesla purchase!). Tesla should be upfront about what it is doing (if the above is in fact true) and be very clear in the user manual that, even though the speedo display reads zero, there are 17 miles left if you drive at 306 watts/mile, or more if you drive with less consumption, AND that using this hidden range is okay (otherwise, if it is NOT okay, then the rated miles shouldn't include it to begin with).

    It is good to hear that I cannot brick my battery that way (as it appears from the explanation that an additional few Kwh are hidden to prevent that, thank god), but I still want an accurate way to know when the car will stop running. Unfortunately, once you reach zero rated miles there is no way to do that other than calculating remaining range by hand and praying.

    You cannot achieve 287 watts/mile traveling at 65 mph at least in my experience under any conditions (maybe downhill or with a strong tailwind but I have never been so lucky). The rated range is supposed to be under real world conditions (and it is, if there is truly always a reliable 17 miles left after reaching zero I suppose).

    The difference though is that in an ICE vehicle, when I run out of gas I can make a phone call and get gas delivered within minutes or an hour tops anywhere in the country. What do you do when you run out of charge (unexpectedly, since the 272 rated miles I get when fully charged would lead one to believe that there was plenty of charge to make a trip, and then some, so long as I maintain about 300 watts/mile) and then the car stops working in the middle of western Tennessee 10 miles short of my destination? Or, more practically, what do you do when 10 miles short of your destination the car reads zero rated miles (again, unexpectedly since the miles were secreted away by the reserve Troll after the trip started). Can you RELY on there being another 17 miles, or should you immediately find a 120V outlet somewhere (ironically, probably a gas station) to get an emergency charge (delaying the final 10 miles by 3 hours!)? That is the real world experience out here, and it is why I think Tesla needs to come clean about this issue.

    It is also not acceptable to say that we should just plan our trips with the safety margin in mind as some have argued. With superchargers, that makes 100% sense. Without them, planning for 20% reserve means I have to spend an *extra* 60 minutes on a public charger above and beyond the 4.5 hours I already know I have to spend to complete the trip (if I can find one within the reduced "safe" range; otherwise, 5 hours extra to charge on a 120V line).

    [/QUOTE]

    The issue with GB numbers in tablets or smartphones that have an embedded OS is similar but with two important differences. First, in the tablet situation I know exactly how much space I have once I boot up the system and go to a command line. With the Tesla there appears to be no way to know exactly how much Kwh (or rated miles) I have remaining; the best I can do is guess or ASSUME that the vehicle will continue operating for 17 miles past 0 at 306 watts/mile of consumption. There is nothing official that confirms this as far as I can tell. Moreover, at any given point in driving I will not know my rated miles remaining with any accuracy without doing a fairly complicated calculation (because rated miles are drawn down faster than the rated 306 watts/mile according to the accepted explanation, but no one can explain how that is done with any accuracy that matches real world data - again as far as I can tell).

    Second, there is the issue that the speedo display and energy app lead you to believe that you have 272 (in my case) miles of rated range so long as you keep consumption down to the rated consumption (306 watts/mile). You drive merrily on your way until you find out that the 17 miles just up and disappeared (stolen by the Troll for the reserve but only after you drive all that way). The analogy would be if you booted up your tablet and it told you you had 16GB of free space, but then when you tried to download a 10GB movie it told you there is not enough space (to further the analogy, you would only find out that there was not enough space after spending an hour and 9GB of your wireless 4g data plan only to have the download abort).
     
  11. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    That hasn't been true for many years (probably more years than I've been alive). The fuel pump intake always sucks from the bottom of the fuel tank.
     
  12. GSP

    GSP Member

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    Maybe not from the very bottom. The Chevy Volt has a 9.3 gal tank but only 8.7 gallons are useable according to GM, if I rember correctly. I think most cars have a similar design. Running a gas car to empty can accelerate wear for some fuel pump designs, since there is not the usual amount of fuel to cool the electric pump.

    Does the Model S rated range really drop from 17 miles directly to zero, instead of 16, 15.....2,1, then 0?

    Most EVs read all the way to zero, unlike gas cars that display "low fuel" when range drops to about 40-50 miles. My Chevy Volt displays EV range all the way to zero. I thought the Model S did as well, and still think it most likely does.

    GSP
     
  13. bluetinc

    bluetinc Member

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    I completely agree with this. While this isn't noticeable in around town driving, I have done a large number of trips that involve driving ~240-260 miles from planned charge point to planned charge point and having a large number of miles mysteriously disappear is what started my collection of data to try to figure out what was going on.


    The 3.9kWh "restricted" portion is only assumed, based on the assumption that the battery has a total capacity of 85kWh when new. This was not confirmed in any way by the community or by Tesla.


    Peter
     
  14. ChadS

    ChadS Petroleum is for sissies

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    #14 ChadS, Sep 5, 2013
    Last edited: Sep 5, 2013
    Hi Jeff,

    I am completely with you that more information from Tesla would be helpful. There is an awful lot of guesswork going on because some details are hidden. I am also a big advocate of EVs having range meters that are less optimistic so drivers are less likely to run in to problems.

    Yes, you can have gas delivered, and it is faster than charging. But I don't know anybody that travels this way because it would still be very inconvenient, and could even be harmful to the car or dangerous to the driver depending on when and where it happens. Running completely out is something you should strive to avoid, no matter what kind of car you drive. It's far easier to get more fuel well before running out - which is leaving a buffer.

    I am not trying to argue with you; I just want to help you avoid frustrating situations (which are sometimes created by optimistic range meters; so we have to set our behavior to deal with them).

    But knowing the absolute remaining range is impossible, so you are going to remain frustrated. (True in a gas car as well, but I will focus on electric here). The car can't predict how the driver will drive. The driver can't always predict hills, winds, traffic conditions, road surfaces, detours, etc. And the car really never knows exactly how much energy it can still pull from the battery. It pulls until the battery gets to a certain voltage level. How much remains can not be measured, and even varies based on environmental conditions, how fast you are pulling, etc. You can't get the exact data that you seek - unless the car fakes it by maintaining a buffer (which is what a pessimistic range meter would do). Might as well maintain the buffer yourself.

    Tesla will not say there are 17 reliable miles after you hit zero, because they are not reliable (if they are there at all, as bluetinc notes).

    Regardless of whether it is acceptable or not, leaving a buffer (no matter what car you are driving) is the only way to make sure you won't run out.

    I agree that the more information we have, the smaller that buffer can be. So I'm with you on hoping Tesla will give us more information. I also encourage owners to learn more about factors that affect range (the link in my signature has more info).
     
  15. dirkhh

    dirkhh Middle-aged Member

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    Hear, hear. I especially want a range meter that DOES NOT LIE TO ME. Regardless what noble reasons there may be. Be self-consistent in what you tell me.
    I have now spoken to four people who ran their car until it stopped moving. And not one of them got anywhere NEAR the 17 miles. The four instances were "2 miles", "around 5 miles", "6 miles", and "almost 7 miles". There's no statistical way this can be a sampling of "on average 17 miles". (ok, putting on my mathematician's hat - yes, of course, there is a minuscule likelihood that this is, indeed, a real sample of a distribution with an average of 17... but come on...)
    Oh, I'm fine with a buffer. I am NOT fine with being lied to. And that's what the range meter is doing. The energy clearly shows me where the 'line' is for rated miles. Yet if I manage to average what that line tells me I do NOT get the range that the rated range tells me. Not even close. And that's my issue.
     
  16. ChadS

    ChadS Petroleum is for sissies

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    #16 ChadS, Sep 5, 2013
    Last edited: Sep 5, 2013
    Yeah, they often end up presenting reality incorrectly. And it can cause serious trouble when they are optimistic and the user doesn't leave a buffer.

    At Plug In America, we've been trying to get the automakers to make their range meters as realistic as possible; and where there's doubt, at least have an option to show the pessimistic range so people don't get in trouble. But you can imagine how excited automakers are about having their cars show less range. Still, I think that's better than having people run out. It's better to have people feel they can rely on new technology, and sometimes be surprised by it working better than expected. (Tesla has said that they are working on a range meter that takes more factors in to account, and so should be more accurate).

    I've also suggested that if they can't say how much is really left, and they don't want to be pessimistic...then don't show remaining range at all. Show remaining energy. You have x kWh left, and you can generally expect 2-3 miles per kWh depending on conditions. Sure a new driver might be thrown at first - but at least they will be cautious until they learn how it works! It's how most gas cars have worked for decades, so it shouldn't take long to catch on.
     
  17. neroden

    neroden Happy Model S Owner

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    #17 neroden, Sep 5, 2013
    Last edited: Sep 5, 2013
    There's a wrinkle to this -- even the kWh is actually an estimate. As we know from cold weather "artificially low" numbers. The car is actually guessing how many kWh are left based on some *other* measurement from the battery (I'm not sure what -- an electrical engineer could proably tell you).
     
  18. vgrinshpun

    vgrinshpun Active Member

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    I agree with you that Tesla should have detailed explanation on the 17 mile reserve in their Manual. I just give them a bit more slack, especially since I now know this and actually unwittingly confirmed this when on my recent 130 mile trip from Lackawaxen, PA to Philadelphia suburbs I hit 286 Wh/mile and had miles traveled exactly equal rated miles used.

    Regarding the "bricking" reserve, Tesla Manual does have detailed description on page 25:

    Never allow the Battery to fully discharge​
    Even when you’re not driving Model S, the Battery discharges very slowlyto power the onboard electronics. On average, the Battery discharges at arate of 1% per day. Situations can arise in which you must leave Model Sunplugged for an extended period of time (for example, at an airport whentravelling). In these situations, keep the 1% in mind to ensure that youleave the Battery with a sufficient charge level. For example, over a twoweekperiod (14 days), the Battery discharges by approximately 14%.Discharging the Battery to 0% may permanently damage the Battery.To protect against a complete discharge, Model S enters a low-powerconsumption mode when the charge level drops to 5%. In this mode, theBattery stops supporting the onboard electronics to slow the discharge rateto approximately 4% per month. Once this low-power consumption mode isactive, it’s important to plug in Model S within two months to avoid Batterydamage.NOTE​
    : When the low-power consumption mode is active, the auxiliary 12Vbattery is no longer being charged and can completely discharge within12 hours. In the unlikely event this occurs, you may need to “jump start” orreplace the 12V battery before you can charge. In this situation, contact
    Tesla.
     
  19. dirkhh

    dirkhh Middle-aged Member

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    You confirmed that on your car "rated miles decrease by 286Wh per mile". You did not confirm the alleged 17 mile reserve. As I said repeatedly, all data I get from people who drove their Tesla until it shut itself down indicates that the reserve is more likely around 4-5 miles, for at least one person it was only about 2 miles (but he was going uphill to his home - and missed reaching his garage by about 200ft).
    Now there's a huge chunk of BS and more lies. 1% per day? IN YOUR DREAMS, Tesla.
    I am now tracking vampire loss as closely as the API lets me and can fairly consistently show about 3kWh loss per day on my 60. So that's FIVE PERCENT​, not one.
     
  20. vgrinshpun

    vgrinshpun Active Member

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    Come on, Peter, we've been through this before - the "anti bricking" portion of the battery is not "only assumed", it is described in the Owners Manual, see my post #18 above (The actual number is 4.25kWh , not 3.9kWh : 85 x 0.5 = 4.25). The "85 kWh battery" mentioned in more than one one place on Tesla Motor site. It does not say 85kWh "usable" capacity, just states that battery capacity is 85kW. This is enough for me to conclude that it is total battery capacity.

    - - - Updated - - -

    I would not be so quick with indignation. The manual I quoted is for version 4.0 software. Is it not true that in version 4.0 the sleep mode was introduced, but later eliminated because of some other unexpected consequences? The sleep mode reduced vampire loss. So the manual may, in fact, have a correct statement. Another thing to consider for vampire loss is whether one uses application during the day to communicate with the on-board systems - this might introduce additional vampir loss as compared with the case when car just sits the whole day and no data flows from the car to one's smart phone application.
     

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