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Ideal charge limit for new MS 85 (100 miles per day usage)

Discussion in 'Model S: Battery & Charging' started by theatwar99, Dec 29, 2015.

  1. theatwar99

    theatwar99 Member

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    Hi everyone,

    Brand new owner of a rear wheel drive Model S 85. I will be using the car 5 days out of the week to commute to my work (50 miles to work, 50 miles to home), mostly driving on Southern California freeways from LA to the Inland Empire (can't wait to use the HOV lane!).

    After picking up the car yesterday at the Service Center, we were given the recommendation to keep the battery charged to 90% (the exception being long road trips), however after browsing this forum, I'm wondering if I should set it to a different limit.

    Obviously I will know more about the car's performance once I start regularly commuting to work (I tend to drive over the speed limit whenever possible, going 80-85 MPH as my commute is largely "against traffic"), but I was wondering with my daily 100 mile commute, what would experienced owners recommend in terms of my battery settings? Obviously as I am really going to be putting a lot of miles on this car I'd like to maximize the life and performance of the battery for as long as possible.

    On a final note, I've really enjoyed lurking in this forum and thanks to everyone for sharing their thoughts on how to make this incredible car even better.
     
  2. TexasEV

    TexasEV Active Member

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    I agree, keep it at 90% and don't hesitate to charge to 100% for road trips. You don't need to obsess over the battery. The battery management system will manage the battery.
     
  3. artsci

    artsci Sponsor

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    I think the consensus among we owners is to charge daily somewhere between 40 and 60 percent, more if a long trip is anticipated. I have no idea why the SC says 90 percent, as that conflicts with other advice given by Tesla. I'm sure others will weigh in with different advice:)
     
  4. BertL

    BertL Active Member

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    OP, as you surmised, you'll get many opinions on this subject. With a few searches, you'll also find a number of other threads where it's been discussed ad infinatum. I spent hours reading and re-reading numerous threads about battery mgmt, watching YouTube videos, and reading technical documents before ordering my MS. I concluded I didn't want or need to be back in Physics class again to own a Tesla BEV, and ended-up deciding Tesla has refined what they either recommend or have as charging defaults on newly delivered MS over time as their own experience has matured, so I'd pretty much go with that.

    I agree with TexasEV you should not obsess over this whole battery management thing. Let Tesla and your MS worry with it. What I do is simple:
    • I plug my MS into my HPWC every time I get home and don't plan another trip the same day. My MS stays plugged-in until I take it out for a ride.
    • I keep my MS set for a 90% charge level, with charging to begin at 12:00 every day when my TOU rates kick in. My MS keeps the charge within 7-8 rated range miles of that 90% level even if I don't drive it for a couple days. My logic here is: My S90D came with 90% as a purposely-designed default in its software, and I figure Tesla and the engineers that designed my MS, who are also responsible for the 8-year battery warranty, must have selected that for a reason. Tesla also has access to more specific information about the battery itself than most anyone on these boards, especially myself. You'll find plenty of people with other opinions and lots of technical explanations, but I personally do not plan to keep my MS beyond 8 years, nor do I live in very extreme hot or cold climates that would perhaps cause me to set my normal every-day charge level lower than the recommendation. I have two exceptions to my 90% level:
    • I trip charge to 100% only when needed for that additional range cushion, and I do it via my Tesla App causing the top-off charge to complete within an hour or two before I leave. I never charge to 100% and leave my MS undriven for an extended period -- that would be bad.
    • If I was going on a long trip of multiple weeks where my MS was going to remain in my garage undriven, I'd drop the charge level to 40-60%, and keep it plugged into my HPWC for my MS to maintain the battery while I'm away.

    It's really easy for me that way ...but you can make it a lot harder if you want to. :) Enjoy your MS!
     
  5. Doug_G

    Doug_G Lead Moderator

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    Pack cycles - or equivalently mileage - clearly dominate over all other influences in PIA's pack capacity survey. Time at high charge and high temperatures theoretically has an impact, but the survey data says it is a small impact.

    Just don't leave it sitting at 100% all the time and you'll be fine. Don't hesitate to use 100% when you need it, but if you don't need it then don't use it.

    Since temperature is a factor at high charge levels, and you have less range in winter, conside charging to 80% in summer and 90% in winter.
     
  6. Todd Burch

    Todd Burch Electron Pilot

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    I recommend 90%.
     
  7. dirkhh

    dirkhh Middle-aged Member

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    I believe Tesla's advice for a long time has been "plug it in whenever you're in your garage and charge to the normal daily limit (90%)". I have not seen any lower recommendation than that from Tesla.
    And at least with v4.x firmware charging to 70% or below on a regular basis caused the range calculation to go weird over time (haven't done this in a long time, so this may no longer be an issue).
     
  8. CLLACAB

    CLLACAB Member

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    If you purchased the car in CA, which you did, our state has pushed the car manufacturers to a higher level. Batteries are warrantied for 10 years/150K mile - full replacement if they fail.
     
  9. theatwar99

    theatwar99 Member

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    Thank you for the recommendations, everyone! Really appreciate all the near instantaneous feedback!
     
  10. TexasEV

    TexasEV Active Member

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    As you see from the above responses, that's not the consensus at all. Most owners only set it 40-60% if it's going to be sitting plugged in unused for weeks. Don't forget that before Tesla introduced the slider in order to avoid EPA averaging the range of two charge settings, the daily use setting was 93%.
     
  11. drsaab

    drsaab Member

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    I drive 100 miles a day. In 1 year did 36 k miles. Charge at 90%. Range was 265 new, Now is about 261 after 12 mos and 36k mi. Seems fine to me.
     
  12. Tyl

    Tyl Member

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    140

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    Here's real world everyday for around town. If you are traveling 100 miles per day, say from 6am to 8pm without any additional charging during the day set 140. In the end you will be your own best judge of what you need. Perhaps you want more heat, have a lead foot, climb long grades, park where it's cold all day. If you travel a regular route, have no worries about arriving home with 5 miles remaining. Charge in the off hours and back to the grind the next day! No need to charge to 90% for no reason!!
     
  13. brkaus

    brkaus Member

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    But there is no proof that charging to lower amounts delays reduces degradation. All we know is sitting at 100% for long periods is supposed to be bad.

    Who knows, perhaps running closer to empty causes degradation as well.
     
  14. Todd Burch

    Todd Burch Electron Pilot

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    There is proof that degredation is higher at higher average states of charge. However (and this is a big however):

    If you charge to 90% in the early morning and drive about 50 miles that morning and another 50 in the afternoon/evening, the car spends most of its day at 75% SOC and most of the evening/night at 50% SOC. If you charge to 140 miles, then that means that a cold, windy, or rainy day might leave you with just a 20 mile buffer. And if you have to do a sudden errand, unexpectedly rush to the hospital (as I did once), or make some unexpected detour, you're going to be screwed, or at the very least inconvenienced. Not to mention that your pack will frequently be run down to the lower end of its charge regime. That's worse for your pack than being at higher states of charge.

    There's no need to cut it that close each day. Driving 100 miles a day, the degredation by charging to 90% is going to be very, very minimal compared to someone charging to, say, 70%.

    In fact, the person with one of the best indicated ranges on this entire forum (Cottonwood) charges to 90% very often, and has even left his pack at 100% SOC for days at a time. And with several tens of thousands of miles on his car (maybe 50-75k?) he still shows close to 265 mi rated range--the range when new.

    With 75k Model S miles now, I can say that (although it's hard) it's better to not constantly worry about your pack. Don't abuse your pack, but don't baby it either.
     
  15. theatwar99

    theatwar99 Member

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    Fantastic feedback. Thank you (and everyone else) for weighing in!
     
  16. mwulff

    mwulff Member

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    I drive a little less than you every day and charge to 80%, thats enough to have me covered if I need to run errands as well.
     
  17. Rocky_H

    Rocky_H Member

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    The recommendation from the sales people of 90% is of course because they want people to have enough range to feel good about using the car, but that’s not them giving a recommendation about what is absolutely best for the long term health and performance of the battery pack. They can’t recommend higher than 90%, because that is specifically recommended AGAINST by the charging screen. 90 to 100 is marked as for trips, and if you use it multiple days in a row, the car will warn you that this is not good. So I don’t see the logic of saying “yeah, use 90%”, when that is right on the edge of the advised against level. There is plenty of research data that a midrange state of charge around 50-60% is best for not degrading most lithium ion battery types, so pick your level somewhere in there between 50 and 90. I usually have it somewhere around 75-80%, where it shows just a little above or below 200 miles. We never get very close to using that up even on long driving days. So that’s a good balance to me of having it near the healthy midrange state of charge, but still having plenty for what I need, including unexpected errands.
     
  18. Electricfan

    Electricfan Member

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    Dang it, that's what I was going to say!

    Well, I do want to add, since this is on the subject of battery care - what I have taken away from all I've read on the subject is this - stay away from the extremes, both top and bottom.

    Don't go near 100% except for trips.

    Don't go near 0% except in emergencies.

    Think of your batteries voltage - that's what you want to keep in a healthy range. If your voltage is low, then the battery must supply MORE current to get the same power level. That's why you don't want the battery to get too low - to avoid straining the battery current. I can't honestly say what the harm in having the voltage too high is, exactly. Maybe somebody can fill this in. I just think of the battery being "hot" when its fully charged, and heat is not good for extended periods. So for the long life of the battery, keep the voltage in a comfortable range - not to "hot" and not flat.
     
  19. mhs

    mhs Member

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    #19 mhs, Dec 30, 2015
    Last edited: Dec 30, 2015
    It's not just SOC - Don't forget the other "big" factor in good battery behavior, and that is charge rate!

    I've been told by Tesla (both the local SC as well as the toll-free service) that the BEST thing you can do for your battery is to charge it slowly so that it reaches your desired SOC soonest to your intended departure time. Try to set a charge rate low enough that your car slowly charges, finishing it's charge in the morning just before your usual departure time. That keeps the battery cells cool and helps to maintain balance between the cells.

    Because of this, I only charge at 80A when I am destination charging.

    For my typical <100 mile day, I charge to 90% using only 20A.

    Also don't forget to do an equalization charge every few months. Charge your car nice and S-L-O-W to 100% and then use it. This balances the battery bank. For me, once a quarter on a Friday night, I will charge to 100% using 5A. When it finishes sometime Saturday morning then I will go for a Saturday morning drive.
     
  20. Oba

    Oba Member

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    #20 Oba, Dec 31, 2015
    Last edited: Dec 31, 2015
    As everybody has stated, most of the advice is quite reasonable, as it is also all over the place. First, as a newbie, I would just charge to whatever value over 50% that makes you comfortable.

    Once you've become accustomed to the actual rated miles used for your daily trip, and you want to maximize the life of your pack, charge it to 50% (about 140 rated miles for an 85/90 pack), plus half your drive.

    Any modern lithium battery has its longest life at 50%, no cycles, and cold. So, anything we do outside those parameters is "harder" on the battery. The worst extremes would be 100% on a very hot day, or 0% in extreme cold (the cells will freeze at about -30C when discharged).

    IDEAL DAILY CHARGE LIMIT:

    (Vehicle Rated Range / 2) + (Daily commute rated miles used / 2) = Daily starting rated miles

    For an 85/90 battery car to drive 100 miles, that will be (280 / 2) + (100 / 2) = 190. You should return home with around 90 rated miles. If you actually burn some greater or lesser rated miles to cover those 100 miles, you can easily adjust.

    No matter what anecdote is shared here (I knew a guy who smoked cigarettes for 80 years, so cigs must be dandy!), the closer you can keep to the ideal, the least amount of degradation you are likely to endure.

    Certainly, don't be afraid to charge up to any value!, even up to 100%, if and when you think you will need it. Temperature is something you have little control over.
     

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