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Bigger Battery = Longer Warranty

Discussion in 'Model S: Battery & Charging' started by WhiteKnight, Nov 2, 2011.

  1. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    Elon Musk said on the earnings call today that if you buy a car with the 300 mile pack you will have a longer warranty than the other packs.

    A Tesla employee explained this to me at the October 1 event. Because the average person drives say 40 miles per day. The 300 mile pack is only cycling 40/300 = 13% whereas the 160 mile pack has to cycle 40/160 = 25% per day. So the 300 mile battery pack will last longer (ceteris paribus) and the warranty will be consequently longer.
     
  2. AnOutsider

    AnOutsider S532 # XS27

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    So does that lend credence to the theory that if you only charge the 300 mile pack every few days (say when you get down to 100m range) then it should also last longer than if you topped off every night?
     
  3. richkae

    richkae VIN587

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    nope
    it could just as easily be the opposite.
    it could also mean more shallow cycles cause less wear than deeper cycles
     
  4. William13

    William13 Member

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    Please, a larger pack means fewer cycles for the same distance driven. Thus longer life.

    Additionally shallow cycles equals longer life for standard Li ion. No memory issues.

    Avoid filling to the top or emptying the bottom of capacity.

    Also we are paying a lot more for the 300 mile. Extra profits. They can reward us with a better warranty. I doubt they will make much money on the base version at first.
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

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    Yep, it's easy math. All of the batteries last roughly 500 full cycles (typical 18650 life). 160*500 = 80k miles, 240*500 = 120k miles, 300*500 = 150k miles.

    Also, with a larger battery and the same power demand, the battery discharges/charges at a lower C rate, which is also easier on the battery.

    Shallower cycles (smaller change in SOC) and staying away from fully charged/discharged is the best for battery life. Thus it's better to charge daily, but keep the SOC near the middle. Tesla sort of does that already in normal mode (where it doesn't let to charge to 100% full or discharge to 0%).
     
  6. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    Will frequent use of the DC fast charging stations shorten battery life?

    I don't know why I think this, but slamming all those electrons into the pack that fast seems like it would not be good for the pack if you did it on a frequent basis.

    You can tell I'm no electrical engineer.
     
  7. Todd Burch

    Todd Burch Electron Pilot

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    Yes...lots of threads on this.
     
  8. stopcrazypp

    stopcrazypp Well-Known Member

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    Yes, the higher the C-rate (where 0.5C is a charging rate that fully charges from empty the battery in 2 hours, 1C is in 1 hours, 2C is in 0.5 hours, etc) the higher the impact on battery life.

    The impact on the battery in these two scenarios are basically the same:
    -42kWh/160 mile battery fully charged in 1 hour
    -85kWh/300 mile battery fully charged in 1 hour

    However, you delivered roughly twice the energy and range to the larger pack in the same amount of time:
    -42kWh/160 mile battery: 42kW/160mph charging speed
    -85kWh/300 mile battery: 85kW/300mph charging speed

    Therefore, given most quick charging stations have a max power rating (50kW for the Leafs), for the same amount of power, a bigger battery pack will be less effected by quick charging than a smaller one.
     
  9. PopSmith

    PopSmith Saving for a Model 3

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    Do 18650's last 500 full cycles even when kept at a near-optimum temperature like the liquid cooling is supposed to do? Also, since most people drive less than 40 miles a day I assume that would mean even the 160 pack would probably "last" 120K or more miles due to much more shallow cycles, right?
     
  10. Larry Chanin

    Larry Chanin Model S Perf Sig 1055

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    Hi,

    Thanks for your helpful remarks.

    Can you please explain why topping off a battery, say at a leisurely rate, would be harmful to battery life.

    Thanks.

    Larry
     
  11. surfingslovak

    surfingslovak Member

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    I believe that the main concern when going above 60 or 70% SOC is the dissolution of cathode material into the electrolyte. The rate of dissolution or degradation increases with the SOC and cell voltage. I gathered some data from research papers on the Leaf forum and although both the Roadster and the Model S use different cell chemistry, I would expect to see similar behavior. There was a nice article on plugincars.com written by Patrick Connor, who happes to be another Leaf owner.

    My Nissan Leaf Forum View topic - Prolonging battery life, temperature, state-of-charge

    Eight Tips to Extend Battery Life of Your Electric Car | PluginCars.com
     
  12. SByer

    SByer '08 #383

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    There are actual physical changes based on charge amount - batteries swell slightly when full. Deep discharges or full charges can cause microcracks that slowly degrade the capacity, no matter how slowly you charge to get there (though slower is better, thus the slowing charge rate near the end of a range mode charge).

    Batteries are complicated ;-).
     
  13. Tommy

    Tommy Member

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    The other point to keep in mind is these 18650's have been specifically made for automotive use vs the generic type that have known parameters regarding charge cycles, shelf life, temperature tolerance, etc. I think we will be in for a pleasant surprise as IMO the automotive grade of battery Tesla is using will outperform the generic in all parameters of battery performance.
     
  14. hcsharp

    hcsharp Active Member

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    In addition to what several other people have said about shallower cycles extending life, when the batteries are at a lower SOC the motor has to pull more amps to produce the same power. More amps means more internal heat in the cells which is ultimately more damaging than storing at a higher SOC.
     
  15. Kipernicus

    Kipernicus Model S Res#P1440

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  16. Trnsl8r

    Trnsl8r Blue 85kwh since 12/8/12

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    Maybe off-topic but... Don't suppose they mentioned how long a warranty they plan to offer for the 300-mile batteries, other than "longer"?
     
  17. surfingslovak

    surfingslovak Member

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    Yes, good article. Note that EV manufacturers usually restrict maximum and minimum cell voltage to prolong life of the battery pack. Although Nissan never confirmed this, we found through CAN bus decoding efforts of a few dedicated owners, that charging to full corresponds to 4.1V and charging to 80% translates to 4.05V in the Leaf. Charging the pack to half full is approximately 3.92V on cell level. If I recall correctly, the Roadster uses 4.10V in standard mode and 4.15V in range mode. Both values are quite conservative, since the cell maximum for LiCoO2 cells is usually 4.2V and for LiMnO2 cells in the Leaf about 4.17V.
     
  18. daniel

    daniel Active Member

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    Another thing to keep in mind: Battery life is defined as the time until the battery's capacity is 80% (IIRC) of what it started out. If you buy a battery pack that has 1.25 times your needed range, at the end of its "life" it will have just your needed range, and will soon drop below it. But if you buy a pack with double your needed range you won't need to replace it until three times its "life." (Assuming degradation procedes linearly.)

    And a question:

    I read somewhere (can't remember where and don't know if this is accurate) that lithium batteries degrade with calendar time even if not charged and discharged. If this is so, the advantage of a big pack noted in my first paragraph would be lost. Anybody know anything about this?

    Finally: I presume that longer battery warranty is just against defects in materials and workmanship. There is no guarantee that the Roadster will have any specified range at any specified time or after any specified number of cycles. While a longer warranty is good, defects usually tun up earlier rather than later, reducing the value of an extended warranty.
     
  19. surfingslovak

    surfingslovak Member

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    This is correct, part of the decline will be due to cycling losses and another part of the decline will be due to limited calendar life. Even though these are custom-built cells, we don't know to what extent they have been optimized for EV applications. Should the cells be similar to regular laptop batteries, then assuming calendar life of six to seven years is a prudent thing to do. Calendar life itself is highly dependent on storage conditions and having a thermal management system, which can be found in all vehicles Tesla designed to date, should help maximize the useful life of the pack.

    NREL did a study on vehicle preconditioning, which includes data on average capacity fade on page 6. I've copied the relevant graph below.

    EV%252520battery%252520degradation%252520rates.png
     
  20. WhiteKnight

    WhiteKnight _____ P85 #549 _____ Sig Red / Sig White

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    Well I heard there would be two warranties.

    One would cover defects in materials and workmanship, etc. That would be the same length for all battery packs. I am guessing it would be 7 or 10 years. Like daniel said, if there's a problem it should show up early so 7 years or 10 years probably makes little difference.

    The second warranty would specifically assure you that you'll maintain 70% of capacity after 7 years or 10 years. So it will be a warranty on your battery capacity / range. In fact it might be something like 90% for 3 years 80% for 5 years 70% for 7 years (maybe it's 5, 7 and 9 years respectively - especially if the batteries lose capacity as a function of time like daniel mentioned).
     

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