TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

Healthiest State of Charge at Rest?

Discussion in 'Model S: Battery & Charging' started by gavine, Mar 27, 2015.

  1. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,010
    Location:
    Southern New Jersey
    I understand that Lithium-Ion batteries don't like to sit at very high or very low states of charge for extended periods of time and I do my best to try and have my car sit as close to 50% charge when not in use. I'm pretty sure that's the healthiest. My question is more about low SOC. Let's say I get home from a trip in the afternoon with 20% battery and won't be driving until the next evening. Is it best to charge up to 50% right away and then higher before my next trip or is leaving it at 20% okay? What is the low SOC threshold that starts to be bad for the battery?
     
  2. Danal

    Danal electricmotorglider.com

    Joined:
    Dec 11, 2014
    Messages:
    431
    Location:
    Fairview, TX, United States
    In theory, immediate charge to 50% and later charge to a higher percent... but.. in practice, simply limiting top level of charge to somewhere below 90% gets you the vast majority of the benefit. The "50 now, more later" is quite a bit of scheduling and worry, for an extremely small gain. And I mean REALLY small. Very theoretical. As compared to 90% charge.
     
  3. djp

    djp Roadster 2.0 VIN939

    Joined:
    Aug 28, 2011
    Messages:
    1,108
    Location:
    Toronto, Canada
    The storage mode in the Roadster maintains the SOC around 20%. It's fine to sit at that level.
     
  4. TexasEV

    TexasEV Active Member

    Joined:
    Jun 5, 2013
    Messages:
    3,790
    Location:
    Austin, TX
    Tesla says to keep it plugged in when possible. No need to obsess over this and not routinely charge to at least 80% if not 90%, unless you're letting it sit for weeks. Let the battery management system manage the battery.
     
  5. stopcrazypp

    stopcrazypp Well-Known Member

    Joined:
    Dec 8, 2007
    Messages:
    7,054
    #5 stopcrazypp, Mar 28, 2015
    Last edited: Mar 28, 2015
    A battery is perfectly happy sitting at a lower SOC than 50%. The reason why it's not recommended is because it reduces the utility of the car since there is lower available range and power (see the P85 threads complaining about performance at lower SOCs).

    The only probable negative is if you purposefully try to reach a lower SOC, you may actually end up with a deeper DOD (which is worse for the battery). For example, instead of charging from 50-75%SOC (DOD = 25%) for two trips, you let the car reach 25% SOC before charging, making your cycle depth 25-75%SOC (50% DOD). The former may actually be better for the battery, despite higher average SOC, because of the lower DOD.

    This factor is probably also why Tesla recommends just leaving the car plugged whenever it's possible.

    There is also higher risk of over-discharge (easier to run the battery empty and permanently kill it). The latter concern was real in the Roadster (which can be "bricked"), but the Model S supposedly can't be "bricked".

    Long story short: Lithium ion batteries don't like sitting at high temperatures at high SOC for long periods of time, and they don't like to be deeply cycled (high variance between maximum and minimum SOC). Those are really the main things to keep in mind.

    A caveat is if you never hit high SOCs or deeply cycle, the battery might more easily get out of balance or the capacity meter inaccurate, which will make it appear to lose significant capacity (although it will come back after being balanced/calibrated).
     
  6. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,010
    Location:
    Southern New Jersey
    Excellent info. Thanks to all.
     
  7. David99

    David99 Active Member

    Joined:
    Jan 31, 2014
    Messages:
    2,058
    Location:
    Brea, Orange County
    Low state of charge seems to be perfectly fine for Lithium batteries. The recommendation for the Roadster to store at 20% shows that. Lowe state of charge is only bad for the battery when you draw lots of power from it. The voltage drops when power is drawn and since the voltage is already lower when the state of charge is low there is a risk that it drops below a certain limit where it becomes bad for the battery. But just sitting at low state of charge is fine.

    If your daily usage is 30% (from 50 down to 20) I would probably charge up to 60% and end at 30% instead of 50 to 20. Quite honestly, if you are driving at those levels your batteries will age very slow, so don't worry about trying to optimize even further and thus making it too complicated.
     
  8. okashira

    okashira Member

    Joined:
    Nov 16, 2006
    Messages:
    120
    0-20%.

    Id actually recommend completely dead for a Model S.
    3.3V / cell is about ideal; and the model S will read 0 rated range at that level.
    I have module sitting like that for weeks/months, and no loss of voltage despite power to the bms board.
     
  9. gavine

    gavine Petrol Head turned EV Enthusiast

    Joined:
    Apr 1, 2014
    Messages:
    1,010
    Location:
    Southern New Jersey
    Very interesting. I wonder why the minimum charge is 50% then. If I go away on vacation and plug the car-in as Tesla recommends, it's going to maintain a 50% charge. I guess the difference in the affect on the battery is so small, it's not worth thinking about it.

    It's great to know that I don't need to worry about charging immediately up to 50% when I get home from a long trip when it's going to charge-up in the middle of the night anyway.

    As was pointed out above, if I were going to head-out again, I would charge-up just to minimize the DOD.
     
  10. okashira

    okashira Member

    Joined:
    Nov 16, 2006
    Messages:
    120
    Precisely. The reason for 50% is Tesla would rather have a more user friendly, consumer friendly battery (ie, ready to drive at all times) that lasts 8-12 years, then a battery that requires baby-sitting and lasts 20+ years.
     
  11. Danal

    Danal electricmotorglider.com

    Joined:
    Dec 11, 2014
    Messages:
    431
    Location:
    Fairview, TX, United States

    More like: Friendly and 3 to 5 years, vs baby sitting and 3 to 5 years. Seriously. No matter what state of charge, Li batteries degrade just sitting. Storage temperature will make much MUCH more difference than 50% state of charge vs. 30% state of charge. No published 18650 cell has a "shelf life" over 3 years, even with 0 cycles and stored at an ideal state (which, BTW, is 40%, per manufacturers data sheets, not 30%). Of course, Tesla/Panasonic are not publishing the EXACT chemistry, we don't know if "100%" according to the car is 4.1 V/Cell, 4.15. 4.05, and more... so don't take ANY numbers too literally... nonetheless, physical age life of more than 5 years would be totally unexpected.

    Bottom line: Don't worry too much. Set charge to 90% except just before travel, and let the Tesla manage its batteries.
     
  12. okashira

    okashira Member

    Joined:
    Nov 16, 2006
    Messages:
    120
    I'm sorry but you are simply misinformed. There is as much as an order of magnitude difference (and more) in degradation rate at 90% SOC vs 0-20% SOC.
    In fact, a Model S cell stored at 10% SOC at 60°C will retain more capacity then one stored at 90% SOC and 25°C.

    That said, the cells are designed for excellent durability in all conditions, so even at full charge, they will outlast almost any other chemistry.
     
  13. Johan

    Johan Took a TSLA bear test. Came back negative.

    Joined:
    Feb 9, 2012
    Messages:
    6,890
    Location:
    Drammen, Norway
    My understanding is that degradation is both due to calendar life and charge/discharge cycles. If you baby the battery with regards to number of cycles, deep discharges, high voltages etc. then it will degrade anyway due to ageing (calendar life). These two effect do not add up, i.e. which ever effect your battery will degrade in a predicatable fashion due to ageing and this happens no matter how much you baby it.
     
  14. Danal

    Danal electricmotorglider.com

    Joined:
    Dec 11, 2014
    Messages:
    431
    Location:
    Fairview, TX, United States

    Link please? I'd like to see a data sheet or white paper from either Tesla or Panasonic that states long term storage numbers. In fact, I'd like to see the exact cell variant/chemistry in use.

    Thanks!

    - - - Updated - - -

    Completely agreed. And temperature at storage has as much to do with it as anything else. If a person is going to expend effort, focus on keeping the battery out of extreme heat, whenever possible, will have the highest rate of return.
     
  15. okashira

    okashira Member

    Joined:
    Nov 16, 2006
    Messages:
    120
    #15 okashira, Mar 30, 2015
    Last edited: Mar 30, 2015
    I Pm'd you the data, as you requested via PM. It's over 1000% difference in degradation rate comparing 30% SOC and 90% SOC for NCA cathode cells, data FROM PANASONIC.

    650% difference for LiCo cathode comparing 0% to 100%.

    The difference is more significant then the difference between 25C and 60C at the same SOC.

    - - - Updated - - -

    I don't know where you are getting this 3-5 year or 3 year shelf life? Maybe for some older cells, true for lead acid or chinese LiFePO4 for sure.
    Panasonic NCA cell would probably last 30+ years sitting on the shelf at 10% or less SOC.
     
  16. ScepticMatt

    ScepticMatt Member

    Joined:
    Nov 5, 2014
    Messages:
    453
    Location:
    Austria
    #16 ScepticMatt, Mar 30, 2015
    Last edited: Mar 30, 2015
  17. okashira

    okashira Member

    Joined:
    Nov 16, 2006
    Messages:
    120
    These are pure gold:

    http://repository.osakafu-u.ac.jp/dspace/bitstream/10466/14150/1/2014900048.pdf
    ^all the info you'd want


    http://www.mdpi.com/2304-6740/2/1/132/pdf

    Post by some guy:
    johnchamplinhall1 | MARCH 28, 2013
    As a Ph.D. physical chemist with 40 years of lithium battery development experience and Model S owner I think I am in a pretty good position to reassure you. The Panasonic cell used in the MS is probably one of the best in the world. I am very familiar with its electrochemical design (LNCA) and have developed physics based models for predicting LNCA life. Providing that your daily driving pattern is reasonable (<100 miles) and its not too hot where you live I predict the battery will last (70% of new range) for > 20 years.
    If you want further reassurance get a copy of the paper below by some Panasonic researchers (you have to buy it for $31). Their results equate to 400,000 miles of life even with 160 mile per day driving cycle
    “Prevention of the Micro cracks Generation in LiNiCoAlO2 Cathode by the Restriction of DOD” Transactions, S. Watanabe, T. Hosokawa, K. Morigaki, M. Kinoshita, and K. Nakura, ECS Transactions 41 (41) 65-74 (2012).

     
  18. Danal

    Danal electricmotorglider.com

    Joined:
    Dec 11, 2014
    Messages:
    431
    Location:
    Fairview, TX, United States
    I stand corrected!

    Excellent data from Okashira, and lots to absorb. Those are indeed pure gold! I've been seeking this data ever since I heard about the Model S. THANK YOU, THANK YOU, THANK YOU!

    Not only that, I'm going to lower my SOC limit, at least for my daily driving.


    Oh, and did I say: THANK YOU
     
  19. okashira

    okashira Member

    Joined:
    Nov 16, 2006
    Messages:
    120
    Look at the phd thesis in my last post

    10%-70% SOC looks best

    0-100% they got ~1200 cycles

    10%-70% looks good for 4000+ cycles! That over 700k miles, almost pointless! lol
     
  20. ScepticMatt

    ScepticMatt Member

    Joined:
    Nov 5, 2014
    Messages:
    453
    Location:
    Austria
    Very interesting, thanks.
     

Share This Page