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Should I really charge SOC to 90% if I drive only 70 miles per day? (85D)

Discussion in 'Model S: Battery & Charging' started by hanl1, Oct 28, 2015.

  1. hanl1

    hanl1 Member

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    I read through through the 'ideal charge percentage' thread, and although it seems that the consensus is to charge at 90% for pack balancing, some people actually advise against doing so if daily mileage is not high. At the risk of re-posting, I would like to gather some fresh opinions from you guys..
     
  2. Polly Wog

    Polly Wog Member

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    You'll get several different opinions, because Tesla simply doesn't tell us directly what the ideal charge percentage is. However, many of us that charge to 90% consistently, as opposed to a lower percentage, appear to be holding on to our rated range better. For example, when I charge (not every day), I almost always charge to 90% (never lower). I have owned my S85 for 19 months and have 22.5K miles, and have only lost 1 rated mile in that time. My 90% is 239 RM (you should be higher, since you have the "D").
     
  3. TexasEV

    TexasEV Active Member

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    Don't sweat whether you charge to 80% or 90% routinely. Just keep it plugged in when you can, and only charge to 100% when you need to and don't let it sit there. Otherwise enjoy driving and let the battery management system manage the battery.
     
  4. Todd Burch

    Todd Burch Electron Pilot

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    I've been driving the Model S since December of 2012. I also drive about 70 miles a day (75-80 usually) and charge to 90% each night. Here are my thoughts:

    1. In the first place, degredation at 90% isn't significantly larger than 80% (for example). For daily charging, the 10% increase from 80% to 90% isn't even remotely as severe to the battery cells as the 10% increase from 90% to 100%.

    2. The original Model S's only allowed around 92-93% SOC as a daily charge initially--so it's clear the original intent was for the Model S to charge daily to that value. In other words, it can't be all that bad if it was originally designed to charge daily to that level. It wasn't until users requested charging to lower levels (such as 50% if the car is going to be sitting around for a longer period of time) that Tesla added the slider for daily charging to lower levels.

    3. Assuming you charge at night (the best way to do it, not only for cheaper electric rates but to help balance demands on the electrical grid), then if your charge finishes sometime in the early morning (such as before you leave to commute to work, for instance) then your battery really isn't sitting that long at 90% anyway. Probably sits there for a few hours at most, at which time you drive about 35 miles (or thereabouts), dropping the pack to about 75% SOC. It stays at 75% most of the day until you drive home, dropping it to about 60%. Then it spends the evening and most of the night at 60% until charging starts again. BTW: I don't worry much about my car sitting at 90% for longer periods on the weekends.

    4. Charging below 90% as you mentioned (and as evidence seems to show) seems to accelerate incorrect calibration of range remaining. Evidence seems to show that this miscalibration can be corrected--it should not be deemed as actual degredation.

    To sum it up, I'd say charge it to 90% and don't worry about it. That seems to be what Tesla originally planned anyway.
     
  5. hanl1

    hanl1 Member

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    Thank you - very clear.
    - - - Updated - - -

    So instead of charging everyday do you recommend charging maybe once every 2 days to 90%?
     
  6. Todd Burch

    Todd Burch Electron Pilot

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    By the way, not sure if you were familiar with the abbreviation, but if not: SOC means State of Charge.

    Anyway, to answer your question: thinking about it from a state of charge perspective, technically it might be better in some respects because that would mean the average SOC for the pack is lower than if you were to charge daily. However, the manual says to plug it in when not in use, and since I assume the Tesla engineers probably know more about the car than I do (a safe assumption I'd say), then I heed the manual's recommendation.

    However, they may have made this suggestion for many other reasons not related to "babying" the battery pack. For example:

    1. Plugging daily ensures you have the most charge buffer if you have unexpected drives crop up. For example, if you have to drive your kid 30 miles to the hospital to get some stitches, you don't want to get in the car and discover that you only have 50 miles left. (Might make getting home a little tricky :).

    2. Plugging daily also ensures that you're in the habit of plugging in, so that you don't forget to plug in when it's really needed.

    3. Following a rule of just plugging in when you can means you don't have to think so much about it--just plug in when you can.

    4. Plugging in when not in use ensures that if you want to pre-condition the cabin via the smartphone app, the car will use shore power (wall power) instead of cycling energy from the battery pack.

    Everything we've seen about the cell chemistry Tesla uses, and the actual real-world pack resilience, shows that as long as you don't abuse the pack, it'll last a long time. I think the takeway Tesla wants you to have is "don't do anything stupid, but just let the pack take care of itself". Don't leave it at 100% for long periods, but don't sweat the details. This cell chemistry seems to be very resistant to degredation.
     
  7. CHG-ON

    CHG-ON Still in love after all these miles

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    I totally agree with Todd and the others. I drive about 25-30 a day-not nearly enough! And I charge to 90 and plug in everyday. I used to worry about it, but don't anymore. I have found that my 90% started at 236mi and has dropped to between 230-232. That may be due to an algorithm change a few months back, as it seemed to happen suddenly. But in reality, with the variability of driving conditions and my own driving inconsistencies with regard to speed, regen, etc., a couple miles probably does not make any difference. When I have been very low on charge, or when I expect to be, I slow down and that makes the biggest difference on remaining range. I used to really watch my consumption carefully. But now I only think about that when driving on a long trip where it might really matter. Net-net is that my car has plenty of range for everything I do. I have never been stranded.

    It takes time to get used to this new way of thinking. You will get more comfortable with it over time until it becomes second nature and then you will think of it in pretty much the same way you think about your gas tank and when to fill up. It did take me time to get there.

    And welcome to the club! You will never regret it nor ever want to go back to the dark side!
     
  8. jlucero

    jlucero Member

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    i also drive around 30-40 miles a day and was wondering the same thing. seems everyone is saying just charge everyday to 80-90% and dont worry about it!
     
  9. J1mbo

    J1mbo Member

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    If longevity is the main concern, try to keep the charge as close to 50% as possible for as long as possible. So charge to 80, 40 miles to work puts it at 60% for the day, drive home puts it at 40% for the evening until charging starts.

    The real damage only happens if you leave it at or near 100% or 0% for a long time..
     
  10. Rocky_H

    Rocky_H Member

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    There are two different questions here, which we need to make sure we know what answer is being given for what is being asked. If you ask Tesla company representatives, they will always tell you “90%”, because the recommended range for the car shows 50% to 90%, so 90 is still acceptable, and they obviously have a vested interest in wanting people to have as much comfort as possible that they will have enough range to use the car how they want and not worry about running out.

    But, if you’re asking about being the most ideal for the long term health of the batteries, that is a different question with a different answer. Lithium ion battery studies for these types of cells show that the best state of charge is around the 50-60% level. Since my round trip commute to work is about 4 miles, and then we may go somewhere in the evening for another 20 miles, I can go a few days at a time without charging, and really don’t have any reason to charge it to 90% every day. I would prefer to keep it closer to the ideal. I think I have it set about 75% or so, which is about 192 rated miles on the display each morning. That is plenty of range for our around town driving with plenty of margin.
     
  11. Majerus

    Majerus Member

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    Wow, i have lost almost 6 miles and about the same mileage 21K and only 11 months.
     
  12. Petra

    Petra Member

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    While this sort of thing is generally true with most Li-Ion chemistries, the trouble is that it's information that applies at the individual cell level... Battery pack SOC is an average and, from browsing here for a while, I gather that we don't really know that much about Tesla's BMS or how it handles cell balancing within the pack. Keeping a pack with this many cells relatively in balance may be a higher priority than keeping the pack SOC within the 40%-80% range, since a poorly balanced pack can hypothetically result in pushing the weaker cells to a progressively deeper discharge depth with each poorly balanced cycle (possibly damaging said cells and compromising the capacity and performance of the pack in the process).

    The lack of detailed BMS information from manufacturers is one of my pet peeves with EVs--it's fine to make it transparent to the user, but provide the information to the users who care/want it.
     
  13. BertL

    BertL Active Member

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    New Low Mileage Owner Charging Approach

    I spent hours, no days, reading and re-reading the many threads (like this one, at least twice) and opinions on this subject while researching before ordering my new MS...

    For perspective, I've had my MS for nearly a month, and I'm a very casual driver: Most days I drive 0-15 miles, a couple days a week perhaps 40-50, and perhaps one or two times a month go on road trips where I'll use most of my charge in a day, or perhaps I'll need to charge while away from home. I live in SoCal -- no extreme climates like those with lots of white stuff on the ground, or owners in climates like Arizona where I lived for a time and it hits 115F+ for days on end during the summer. I'm an anal kinda guy when it comes to taking care of my rides in just about every way, and keep them generally 5-8 years. The way I'm approaching MS charging is:

    - I plug my MS into my HPWC every time I get home, if I don't have another planned errand that day; Charging begins at 12:05AM if MS decides it needs it, so I get the best rates; With my dual charger and 100-amp circuit, I could fully charge my "empty" MS to 100% before the cheap rates end each morning (That was a purposeful decision on my part before I ordered my S90D and set up the electrical in my garage. Is it overkill, perhaps yes to a large degree, but I have no anxiety about possibly not having a charge in an emergency and I don't have to overthink it either).

    - I leave my MS at the 90% default charging level

    - If I'm going on a major road trip (only once so far), I use my Tesla App to bring the charge up to 100% when I wake up in the morning, then take off within an hour or two at most when I'm ready

    - I would only bring my default charging level down to 50% if I were going out of town for several weeks and was going to leave my MS parked in my garage the whole time​

    I too figure if Tesla Engineers who design MS and are responsible for it's 8-year warranty went to the trouble of building the 90% default, setting the car to that default upon delivery, and say in the Owner's Manual to keep MS plugged in when not in use, who am I with my limited engineering knowledge of a Tesla Battery to do something different. Also, I think sometimes enthusiasts can overthink things -- I sure do some times -- but in this case, I believe the KISS method (Keep It Simple Stupid) approach is best for me. I don't plan to keep my MS for the rest of my life, but I do expect that my battery range, especially with the 8-year warranty my MS battery has, will not be a problem as long as I own it, and likely not for whoever owns my best toy after me.
     
  14. rdrcrmatt

    rdrcrmatt Member

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    I used to drive a lot, 150-200 per day. I'm almost at 72,000mi. Now, only 70-100. I charge to 70% daily and schedule my charges to end around when I'm going to leave.
     
  15. Rocky_H

    Rocky_H Member

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    That's true, but since that is such an important factor, I am absolutely certain that Tesla were not idiots in designing their battery and battery management system where it could get really out of balance and damage cells and it is up to us customers to have to know about it and find out the ways to charge a certain way to fix and prevent it.

    And to add to @BertL’s comment, about 90% being the default, I would refer you to the charging screen in the car, where you set the level: It shows a range for “Daily” use, and a range for “Trip” use. They do advise with warnings to not use the “Trip” area all the time, but only as needed. The recommended daily range is 50% to 90%. So I don’t quite see why people think 90% is what it should be all the time for daily use. That is right up there at the maximum level of the Daily range and is on the border of the Trip range that they advise against using all of the time. It just makes a bit more sense to me, to move it down a couple ticks to not be right at the very top edge of the recommended 50-90.
     
  16. JMG

    JMG Member

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    Consider yourself lucky. My 85D with 13,000 miles has lost 13 miles of RM from a 100% charge. When I picked it up in May, they charged it to 100% and it had 273 miles (range mode on, not sure if that makes a big difference or not). Just yesterday when I charged to 100% (which I do very rarely), it was at 260 miles. I'm a little nervous with an almost 5% drop in 5 months.
     
  17. Polly Wog

    Polly Wog Member

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    I don't charge every day because I have a somewhat unique charging situation and it simply isn't convenient to charge every day (see link to my setup, if curious). With that said, given how fortunate I seem to be with holding on to my rated range, I don't plan on changing my charging habits. I charge to 90% roughly every 2-3 days, and I am usually at about a 60% SOC when I do charge.

    http://www.teslamotorsclub.com/showthread.php/55500-Creative-Condo-Charging-Solution
     
  18. tezco

    tezco Sig P85

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    I usually only take the S out on the weekends and charge back to 50% after a drive, then I unplug the car. Before I'm set to go out again I charge to a level (usually around 70 or 80%) that will leave me not too far under 50% by the time I get home. So normally I only charge once a week. About once or twice a year I charge to 100% immediately before a trip. We've only lost a few rated miles since we got the car in 2012.
     

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