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Percentage Question

Discussion in 'Model S: Battery & Charging' started by donv, Jul 10, 2015.

  1. donv

    donv Member

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    If I show available range as "Rated" (in the US, anyway), I believe this to show, based on a certain energy usage rate, how much energy is in the battery.

    Now, if I switch to percentage, what is the percentage showing? Is it showing percentage of original capacity, or percentage of available capacity?

    In other words, if I have a 5% degradation in the capacity of my battery, will it charge to 100%, or just 95%?

    Presumably the rated range would show the degradation (or else I would never know it's happening), but is it reflected in percentage as well?
     
  2. TexasEV

    TexasEV Active Member

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    The percentage is the percentage of your battery capacity, so it will always charge to 100%.
     
  3. donv

    donv Member

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    So, in other words, if you only looked at percentage you would never know about battery degradation?

     
  4. Chipper

    Chipper Active Member

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    Correct.
     
  5. kennybobby

    kennybobby Member

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    It's just an indicator like a fuel gauge, F = Full (100%) E = Empty (0%).

    If you drive fast on the highway, hard acceleration starts or lots of hills to climb you get less miles of range for a Full 'tank' than easy starts and slower city speeds, just like any car behaves.

    If you want to know actual capacity, then you would need to make a calibrated measurement following a specific test procedure.

    If you wanted to determine degradation then you would make this calibrated measurement periodically and plot the capacity versus time or versus number of charge-discharge cycles.
     
  6. ecarfan

    ecarfan Well-Known Member

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    Yes I think that is correct. It is a percentage of how much rated range you have at that moment out of the maximum possible range you would have if the battery was charged to 100% at that moment.
    It cannot be used to measure battery degradation. If you want to estimate degradation, compare a current maximum range on a full charge to what it was at some earlier point in time.
     

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