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The Right Daily Charge Level

Discussion in 'Supercharging & Charging Infrastructure' started by Ed Hart, Dec 16, 2018.

  1. Ed Hart

    Ed Hart Member

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    OK...I am confused. Earlier in the Year, I am sure I heard Elon answer a question about the recommended daily charge level, to which he said 70%. Then last week, I believe there was a tweet from Elon that recommended 90%. So....which is it?!
     
  2. ronm2948

    ronm2948 Member

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    I’ve read a lot of people’s opinions, and I don’t think there is a straight-forward answer to this.

    Pretty much everyone agrees that having your car at close to 100% or close to 0% for extended periods is not good for the battery.

    And batteries will degrade over time, regardless of how you treat them.

    So the question is how much of a difference does different charge levels make?

    My personal belief is that the difference between 90%, 80%, 70% does exist (with lower charge levels being better for the battery), but it is probably not worth worrying about. Maybe after 5 years, it might make the difference of a few miles of range, but not much more than that. This is not based on any scientific facts, but just my feeling after doing a lot of reading.

    My M3 is set to charge to 85%.
     
  3. Ed Hart

    Ed Hart Member

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    Thanks, Ron. With no other guidance, but based on Elon's last tweet, I set both my 2014 MS and 2018 MX to 90%, which appears to be the recommended daily maximum on the charge level setting in each vehicle. I had been charging to about 80%. The 2014 Ms has nearly about 70,000 miles, most of it here in Southern California. So far, I appear to have lost less than 1% per year of range.
     
  4. GSP

    GSP Member

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    Model 3 owners that charge to 70% daily, including myself, have had our GOM rated range drop significantly. Mine went from 310 miles to 260. It seems that the Model 3 BMS needs to be charged to 90 or 100% for the software to estimate battery capacity accurately. Charging to 100% a few times fixed the low range displayed on my 3.

    While charging to 100% helps all BMS software estimate capacity better, the Model S and X do not seem to require it as often as the 3.

    Since Prof. Jeff Dahn (respected battery researcher employed by Tesla) recommends 70-80% for daily charging, I still charge my S to 70-80%. I now charge my 3 to 80-90%. I use the lower values in the summer, when low SOC is more helpful to prolong life.

    GSP
     
  5. Rocky_H

    Rocky_H Well-Known Member

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    There is not just one answer for the perfect single point for all use cases. It depends on what you want to do:

    (1) If you want to treat your battery the best, but never use your car, then about 50% is best ideally for the battery.
    but
    (2) If you want to actually use your car, then you probably want a higher state of charge than 50%.

    So that's why they show the "Daily" range on the charging screen as 50% to 90%. You balance those two priorities and pick as to what suits your use. Toward the lower end is better for the battery, but toward the higher end is more miles for you to drive with and less range anxiety.

    But keep in mind, that how much better for the battery is not totally linear. For instance, a 10% reduction in state of charge does a lot when you're moving from 100% to 90%, but isn't making much difference if you're going from 70% to 60%. The first bit of moving away from the extreme top end has the most impact.
     
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  6. Rocky_H

    Rocky_H Well-Known Member

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    Huh. My explanation of the two differing priorities people need to balance to come up with their charge limit got a disagree. Someone doesn't like having to make decisions?
     
  7. SSedan

    SSedan Active Member

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    When I first got my car last year I set it to 90% had been at a Ford dealer for quite some time and I believe they were letting it run down then taking to a supercharger. Appeared to have 3.5% degradation at 3yo 65k then I set the daily charge to 70-80% and it appears I lost nearly 20miles of range since doing that. I say appears because I am reasonably confident that if I run it down and charge above 90% a few times much of that will come back.
    My P85 charged to I believe 257 when I got it last year but only 238 a week ago, I believe it is just calibration not a 20mile loss in 15k miles of use.
    I charge every day and only put on 15-35miles most days. The shallow discharge and low charge limit seem to be prone to BMS calibration issues.
     
  8. GSP

    GSP Member

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    I am often surprised and amazed with the things that people will vote down with a disagree. After taking the time to try and be helpful, it seems like no good deed will go unpunished.

    My theory is that some people are just disagreeable by nature.

    GSP
     
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  9. Big Earl

    Big Earl bnkwupt

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    Split the difference at 85% and enjoy life. :)
     
  10. SabrToothSqrl

    SabrToothSqrl Active Member

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    it's 90.000000000000000000000000000001%

    no more. no less.
     
  11. Ed Hart

    Ed Hart Member

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    Good discussion. I am going to keep mine charging to 90%, and see what happens. At 70,000 miles, my losses appear to be in the range of 1-1.5% per year, so far. Better than I expected.
     
  12. zhu-

    zhu- custom title

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    70% is still better for the battery, but the 90% recommendation is due to the overall convenience of increased range and more accurate range estimates with a nominal increase in battery degradation.
     
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