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How much better is 80% instead of 90% for the battery?

Discussion in 'Model S: Battery & Charging' started by hingisfan, Aug 26, 2015.

  1. hingisfan

    hingisfan hingisfan_Mark_V

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    I just have a 60. In winter, I need daily charging to 90%, but in summer I can usually get away with 80%, but once in a while I cut it too close and I have to top up during the day, making we regret not doing my daily charge to 90%. This probably happens once every two weeks or so.
    So, am I really doing my battery a big favour by charging to 80 instead of 90 for 7 or 8 months of the year? Or is this not really a big deal? I do plan on keeping the car long term.
    Thanks!
     
  2. gaswalla

    gaswalla P4201/85/airsusp/pano/19i

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    Many folks have concluded that consistent 90 percent charging keeps the battery better balanced. You may see an ongoing 'loss' of range by charging to less but it is recoverable by charging to 90 multiple times
     
  3. dsm363

    dsm363 Roadster + Sig Model S

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    If it actually forces you to charge during the day and that is an inconvenience than just charge to 90%. The difference if there is any is likely very minor
     
  4. Brass Guy

    Brass Guy Member

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    From what I have gleaned during the past couple of years, if you are dipping into the last 20% of the battery you're better off charging to 90% daily.
    Keeping the SOC between 80% & 20% is great, but 90% to 20% is better than 80% to 10%. Using the bottom 10% is probably worse for degradation than using the top 10%.
     
  5. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    I charge to 90% daily and don't even bother thinking about it anymore. For trips I charge to 100%, and the only thing I do is try to minimize the amount of time the pack sits at 100%.
     
  6. aja2460

    aja2460 Old Member

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    Come on now... it's not 'just a 60', it's a Tesla.
     
  7. DaveVa

    DaveVa Sig Perf #236 VIN #484

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    When the car was first released Tesla battery options were a "switch" instead of a "slider". The two choices were Trip - 100% and Normal - @~92%. It was only at the request of the user community that they put in other options. I think in Tesla's experience 90% was fine for daily use...
     
  8. hingisfan

    hingisfan hingisfan_Mark_V

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    Thanks guys... I'll just switch to 90 year round... I do have a supercharger 20km from me where I am usually driving so its not a huge deal to pop in for 10 or 15 min.... But, I guess that's 'abuse', lol.

    - - - Updated - - -

    I know... I'm actually pretty proud that I restrained myself from ordering new and got a 4 month old, 12,000km Tesla for 65k CDN... Base 70 rwd would now be 82k here new. No AP though, but it's all good.
     
  9. Rocky_H

    Rocky_H Member

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    I don't think anyone is going to be able to quantify that for you on your initial question "how much better?".
     
  10. WarpedOne

    WarpedOne Supreme Premier

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    Hove much batter?
    3/4 of some minus slightly.
     
  11. LetsGoFast

    LetsGoFast Active Member

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    Do you have a source for this? There is a very clear linear relationship to degradation at higher SOC and temperature, but degradation at lower SOC can vary a great deal, particularly depending on exactly where Tesla sets their low voltage threshhold. They have control of what point they declare the battery to be at zero and knowing where they set that point would be important to establishing the risk of lower SOC use. The difference is probably quite small, but I'd guess that 80-10 is marginally better than 90-20. I'd love to learn more -- have Tesla ever elaborated?

    They probably just want you to rely on their BMS and not to think about it, so they may avoid providing any information. Its all quite small differences in any event. If you charged to 90% every day and your clone charged to 80% every day, the difference would likely be far less than 1% over the useful life of the car anyhow.
     
  12. bhzmark

    bhzmark Active Member

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    An old elon tweet suggested 80 or 85 was better than 90. Does anyone remember that or have link?
     
  13. apacheguy

    apacheguy Sig 255, VIN 320

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    I'm not sure I understand this. According to okashira, the cells are perfectly happy being stored below 20%. Heck, storage mode on the roadster is 20%. Not sure I understand why low states of charge are undesirable.

    What do folks do if the car must idle for several hours in excessive heat? Does heat impact your daily charge limit at all?
     
  14. jerry33

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

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    Low SOC is undesirable when driving because the cells heat up more for any given amount of power compared to higher SOC.

    I thought the storage mode on the Roadster was 50%???

    The way I work the excessive heat is:

    - Set the timer to start the charge at 02:30

    - Charge to 80% which finishes shortly before I drive to work.

    - It's sits most of the day at 70%, and then at 60% from when I arrive at home (typically ~16:30) until 02:30.

    - I don't worry about changing it for the weekend unless I'm going to require more range.

    - Yes, I could charge even lower, but if I'm called into work or the power goes out (deregulation is so wonderful), charging to 80% gives me a decent cushion.
     
  15. bollar

    bollar Disgruntled Member

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  16. apacheguy

    apacheguy Sig 255, VIN 320

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    Ok, yeah, sounds good. I usually leave it less than or equal to 70% in the heat.

    WRT low SOC and heat generated, isn't that what the BMS is for? Liquid cooling and limiting the power draw from the pack? Sure, I can see how there's some effect, but I would expect this to be very minimal given the operating constraints enforced by BMS.

    And looks like you're right WRT storage mode being 50%. I could've sworn it was 20:

    Vacation Storage Mode | TESLA OWNER
     
  17. LetsGoFast

    LetsGoFast Active Member

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    When asked which was better, driving from 90 to 40 every day or 80 to 30, Elton replied 80 to 30

    Twitter
     
  18. Knobby

    Knobby Member

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    This is exactly what I see. Was charging regularly to 70% and the range has diminished over time. If I charge to 100% a few times, it recovers most of the lost range.
     
  19. djp

    djp Roadster 2.0 VIN939

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    You were right the first time, storage mode in the Roadster is 20%. I use it every winter. There's nothing wrong with storing at low SOC. It's driving hard at low SOC that's tough on the battery.
     
  20. David99

    David99 Active Member

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    Honestly I don't think the charge level is that important. If you drive off right after you finish charging, it's totally fine. So instead of trying to predict the exact amount you need, it helps the battery long term life much more to use the charge timer and set it so the car finishes charging just a little before you leave in the morning.
    It's bad to charge the battery and let it sit at high levels for a long time. What is 'a long time'? Look at it this way: You charge it right when you come home at 6 pm and it finishes at 11 pm, then it sits there for 8 hours. Since you are doing it every day, it adds up to 'a long time'. If you use the charge timer, the car sits at a lower state of charge for those 8 hours and then gets charged. Again, since it happens every day, this time adds up.

    It would be very very useful if Tesla would finally have a charge timer that let's you input the time you need to leave and it figures out when to start charging on it's own.
     

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