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What is the correct maximum battery charge to set? 85%,90%,95%,97%

Discussion in 'Model X' started by Cwsnhri, Apr 25, 2016.

  1. Cwsnhri

    Cwsnhri Member

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    I have set mine so I charge to 249 mi. Thoughts?
     
  2. Keith

    Keith Member

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    I've been wanting people's thoughts on this as well, I've been setting mine to 80% , but have been considering 70% or 60% since I don't need the extra range on a daily basis and assume the lower SOC is better (if slightly) for the longevity of the battery.
     
  3. tstafford

    tstafford Member

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    My understanding - 90%. Tesla told me this and I believe this is what most folks do. I only charge above that for road trips or other special occasions and I try to make sure that I drive the car shortly after it hits 100%. I believe the harm to the battery is sitting around at 100% more so than reaching 100%.
     
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  4. swesson

    swesson Member

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    Set it to what you need. 50% might be just fine.
     
  5. wdolson

    wdolson Active Member

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    Most rechargeable batteries are touchy about how they are charged. I believe Li-ion are happiest if they are charged up to around 90%. As tsstafford said, it's fine to charge to 100% if you are going to drive the car right away. In fact some people have reported range degradation can be reversed to some extent by charging to 100% once in a while. The explanation is rather complicated, but kmanauto goes into it in detail in a couple of his videos.
     
  6. gaswalla

    gaswalla P4201/85/airsusp/pano/19i

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    4 year Model S owner here: Tesla Service has repeatedly recommended 90% daily charging for best battery health.
    With my minimal degradation after 113K on an "A" battery, I have to agree
     
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  7. jdw

    jdw Member

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    I believe usage pattern plays a role as well.

    If you have a daily commute of any size, then timing a charge to 90% to finish just before you leave means you have a decent available charge everyday, plus the car spends most of the day at 70-80% or less. Since high state of charge and high temperature are the enemy of batteries, minimizing that combination is likely somewhat important. When it is really hot, I often only charge to 90% every second day, further lowering the sitting state of charge. Shallow charge and discharge cycles are also better for battery health than deep discharges.

    Charging to 90% daily, with the occasional range charge, keeps the capacity/algorithm calibrated. I see no point in charging the car to 90% when I get home and leaving it sit at that level for 12+ hours. If I know I won't be driving much for a few days, I also delay charging as above.
     
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  8. Hengist

    Hengist Member

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    The best for daily use is to have your starting and ending state of charge about equally distant from 50%. So if you drive 100 miles a day, you want to be at about 175 miles range in the morning and end up at about 75 miles in the evening. The batteries are least happy at hot temperatures or very cold temperatures when they are at very low state of charge. When really full, they don't like hot or extreme cold either. MUCH better to charge to 100% 257 miles, and end up at 57 miles than to charge to 200 miles and end up at zero.

    This is one of the best reasons to have the 90D rather than 75D: you can cycle around 50% with less chance of getting really low.

    Above based on three years experience in Model S.
     
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  9. loganintx

    loganintx Member

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    Tesla warranties the batteries for 8 years unlimited miles and they recommend charging to 90% every night. I'm just going to do that and not worry about it.
     
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  10. X Fan

    X Fan Member

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    Makes sense...I wonder if lease holders are as diligent.......
     
  11. int32_t

    int32_t Tesla Spotter

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    Yep, based on my experience and research regarding lithium battery tech, not storing while fully charged or completely empty is important for long life. The other most important thing is to not be afraid of full charges because the battery was designed to give you hundreds of kilometres of range. What's the good of that if you only ever charge to 80%? I wouldn't charge to 100% and let it sit for a week before my trip, but I wouldn't be like, "I'm leaving at 9 AM so I'll schedule it to finish charging at 8:59" either.

    Consider this Apples-to-Oranges comparision from Apple's lithium battery tech:
    iPhone 5, 2012 - with a full charge I can expect 5-7 hours of usage.
    iPad 2, 2011 - with a full charge I can get 11-13 hours of use.

    Both of these are with Wi-Fi on and the display at a comfortable brightness. The main difference is the under-the-hood battery management. To make the iPhone more compact, Apple allows the user to access more of the battery's capacity, like charging from, say, 2% to 98% of the battery's total energy capacity. With the iPad, things are a little different: the user might be able to access the 6-7% to 93-94% range of the battery's total capacity, which is a smaller window (is this making any sense?). This isn't purely anecdotal either, the cycle life ratings for these two products are actually quite different. If my memory serves me correctly, the iPhone's battery is rated for ~500 cycles whereas the iPad is rated for 1200 or 1500 cycles before dropping below 80% of initial capacity. Hardly a coincidence, in my opinion. The only way to do this is to limit the battery capacity available to the user.

    So Tesla is doing something much like the iPad which will prolong the battery's serviceable lifetime, but also allows you the advantage of accessing the additional capacity when you need it. Charging the battery to full every day (like what happens to your hapless phone) is probably what would kill it faster, but 90% is a good reasonable number (I'm certain it's more conservative than the iPad, actually).

    Pictograms, anyone?

    [----------------} iPhone (virtually all available)
    [=-------------=} iPad (top and bottom 4 or 5% reserved and never used)
    [=------------==} Tesla (bottom reserved, top limited by default but accessible for road trips)

    Hope this helps understand what's going on and why Tesla doesn't recommend fully charging all the time. I also hope you won't be afraid of the odd range charge since that's what it is for, after all. Mind you, I have heard of people range charging all the time with no extra noticeable degradation. (And I suspect the recovered estimated mileage after a range charge has something to do with battery balancing, but that's a topic for another day perhaps.)
     
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  12. tstafford

    tstafford Member

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    Probably not on whole. (I am but I'm a rule follower type). One of the main reasons that high end manufacturers (BMW, MB, etc.) went to free scheduled maintenance was to alleviate this concern for buyers of used, CPO cars - in many cases lease returns.
     
  13. mercc3650

    mercc3650 Member

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    I charge to 90% now, but I also don't recharge on a daily basis, but rather every 2-3 days as my daily driving is 40-60 miles.

    I don't know if this is a good thing to recharge every couple days, or is it better for battery life to bring the battery back up to 90% for better battery health.

    Advantage of every 2-3 day charging:
    - don't have to plug in nightly
    - can use summons every morning with home link to open garage, back up the X and close the garage from my phone while drinking my coffee in my kitchen watching the show
     
  14. CTemp222

    CTemp222 Member

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    I've heard that not charging the battery at all prevents battery degradation 100%! ;)
     
  15. Keith

    Keith Member

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    Just a note: Tesla recommends that you keep your car plugged when not in use so the battery management system can heat or cool the battery pack to keep it at an optimal temperature.
     
  16. bxr140

    bxr140 Member

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    For the same amount of miles (or kWh), more smaller charges are healthier than fewer big charges...or at least so I've read on TMC.

    Those with the ability to charge every day should do so.
     
  17. daxz

    daxz Member

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    see this thread: Why do Li-ion Batteries die? And how to improve the situation?

    specifically look at post #17 (I lower cased quote to make it read easier)
     
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  18. Keith

    Keith Member

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    My X spends most of its time plugged in, so I keep my charge a little lower since I also don't need the range. Lately I've been doing 70% and it's been difficult mentally (I like to see a full battery for purely aesthetic reasons), but practically I still don't drive enough to see my charge fall below 50%. What @daxz said about voltage in relation to SOC makes a lot of sense.

    It would be nice to know for sure how an average SOC affects cell longevity in the Tesla battery pack. However it seems that since Tesla added lower charge limits (to 50%), it was probably for a reason, I'm just surprised that everyone is saying that Tesla recommends 90%.

    I've read elsewhere that 50-62% is the ideal charge range for the Tesla, so maybe work with that?
     
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  19. jerry33

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

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    The 50% is really for long term storage. As far as I know, the biggest benefit is not setting it above 90%. Each additional 10% lower adds progressively less benefit to battery life. Originally, Tesla just had ~90% daily and 100% trip, but the way the EPA rates the cars sort of forced them to put the slider in, or take the Leaf route and just have 100% charging (which is far from ideal).

    The main problem with a lower charge level is that the pack goes out of balance, so once a month or so charge to over 93% and then drive right away so that the car doesn't sit at a high charge level. Once the balancing is started (triggered by the 93%) it continues until done over several days regardless of charge level. (This info is from WK57 who's done a lot of research on the battery.)
     
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  20. UberEV1

    UberEV1 Member

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    @jerry33: Good reminder!

    For those new to Tesla and/or to the TMC Forum, this topic was very popular several years ago as some of us early adopters tried to understand and explain changes in battery capacity (total range). As Jerry33 points out, the pack goes out of balance, which basically means some of the battery cells drift to a lower stored energy level compared to others. When charging above the trigger point, circuits inside the pack direct the stronger cells to trickle charge the weaker ones to bring them all back into balance. The net effect is a slight gain in maximum range, and likely better health for the pack.

    At first, some of us thought that our packs were degrading too quickly. It seemed packs that were routinely being charged to levels below 90% would show faster apparent degradation. Then we learned that this was likely due to the pack balancing circuit never being triggered. Several forum members reported that by returning to 90%+ charging over several weeks, they could regain some or almost all of their range, thus reinforcing the pack balancing explanation. Personally, I saw this same effect on my 2013 "B" pack. My own algorithm is to charge to 90% when I am in town, and to 75% when the car is not in use (no clue if this is best, but my B pack seems pretty healthy).

    So, in short, avoid hanging out at the extremes of 0% or 100% for any length of time (certainly OK to charge to 100%, but then start driving soon so it does not sit at 100%). If you feel your range is declining, try charging to 93% for a week and see if range increases. Losing 3~5% of max range over the first year is pretty typical, but many have reported that it seems to stabilize after that.

    By the way, WK057 was one of the first, if not the first, to completely disassemble the battery pack and understand construction, connections and operation. If you are technically curious, you may find it interesting looking through his posts.
     
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