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How much to charge for durability of the Battery

Discussion in 'Model S: Battery & Charging' started by Realistic EV Fan, Aug 26, 2014.

  1. Realistic EV Fan

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    There has been a lot of talk about how to charge the battery to extend the life. I'm not sure the battery can even be extended past 10 years of life since lithium-ion batteries are also prone to degradation just by time. But I'm wondering is it better to charge to the minimum highest state of charge that is required for the daily commute with some buffer of course? Or is it better to charge slightly more to avoid running the battery below 20% state of charge as it does not seem to like it there from what I heard? The commute is 40 miles one way and of course 40 miles back but this can be an extreme weather of almost -45°F. Nobody has any information on this or experience
     
  2. WeazL

    WeazL Moderator - Hawaii

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    I would suggest following Tesla's recommendation of keeping the vehicle plugged in when not in use and let the on board system do the work of deciding when to charge. Note that Tesla does not recommend charging to 100% daily as it degrades the batteries faster.

    If Tesla is confident enough to put an 8yr full replacement warranty on the battery (as it has on 85 kWh and higher), I'd bet that they're confident it will last quite longer than 8 years. They wouldn't assume that much risk on a 2-year window.
     
  3. mgboyes

    mgboyes Member

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    Very low states of charge are bad for the battery and should be avoided if possible. Very high states of charge are slightly bad for the car and should only be used when needed. Everything in between is fine.

    Just relax and let the most advanced battery management system in the world do its thing.
     
  4. David99

    David99 Active Member

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    Lithium batteries age faster the warmer it is and the higher the state of charge is. It's a chemical reaction inside the batteries that happens to kill the battery. The higher the battery is charged, the faster it happens and higher temperatures accelerate this process. Elon once said the batteries would last 'forever' in Alaska. A very knowledgeable professor (one of his students now works as Tesla) said, if you keep a Lithium battery at 30%, you can store it for years and won't see much degradation. But a very low state of charge is not good for the battery especially when driving. So it is recommended to stay away from both ends of the charge level.

    If you only need 80 miles I would charge to 80 miles plus 30%. This way when you are done driving for the day, you arrive with 30%. I think 30% is something like 78 rates miles. So you would charge to 78+80=158 rated miles. You mentioned you are dealing with extreme temperatures and weather. Even if your distance is 80 miles you might end up needing 110 rated miles. So you would charge to 110+78 = 198. Test it out and see how much you use and then add that to the 30% marker. That's what I usually do.

    BTW, when the battery is at 0 rated miles, it is not completely discharged. It is not really at zero. It's 76.5 kWh from from 100% to 0%. I have tested this a few times. That's exactly 90% of the rated capacity of 85 kW. In other words the car hides the lowest 10% which you should never use. If you really really have to, you get another 5% out of it, then the car shuts down. So the car will never allow you to completely drain the battery as it would damage it.

    The battery warranty doesn't cover normal aging/degradation of the battery. There is a lot of very good information out there about lithium batteries. Nothing wrong with using that knowledge to get a little more life out of a battery that is very expensive.
     
  5. ecarfan

    ecarfan Well-Known Member

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    @Realistic, I don't live in a cold climate like you have, but based on what I've read on TMC (and there have been many discussions of the issue you raise) in extreme I would charge to slightly double the range of your planned 80 mile trip and you will likely end up with a nice buffer when you get home, something above 20% SOC. Then plug in and let the cars software do it's thing to manage the battery.

    Most importantly, don't overthink it and don't obsess about it :)

    And I second @WeazL's sound advice.
     
  6. Realistic EV Fan

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    The one factor that has to be factored into the equation is the degradation factor. So many miles of charge might not pushed the battery to its limits when it's brand-new. But as it starts to degrade, that same charge state is going to push the battery more and more into the extreme zone of very high and very low state of charge. This of course accelerates the degradation process. So one really has to think what has been needed charge and how is but a comfortable charge for the battery once it starts getting degraded. For sure to 160 mile charge might not pushed the battery when it's brand-new, but take it eight years down the road and this might be pushing the bounds of what the battery can take. This is one of those unfortunately unknown factor as of now. Unfortunately only time will tell, and that is hard to plan for today.
     
  7. jerry33

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

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    With luck, there will be more Superchargers (and HPWCs) so that might not be as big a problem as it would be today.
     

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