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What should my ideal charge percentage be?

Discussion in 'Model S: Battery & Charging' started by Al Sherman, May 19, 2013.

  1. Al Sherman

    Al Sherman It's about THIS car.

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    Given the introduction of the "slider" I would like Tesla to give a number (percentage charge) that is optimal for the life of the pack. If you never (or almost never) need the full, or even standard charge range; what is the best level to charge to on a daily basis? Most driving days for me are less than 30 miles. What's my number? I'm certain it wouldn't totally end speculation. If Tesla engineers came up with a number for this scenario it would end any speculation for me.
     
  2. djp

    djp Roadster 2.0 VIN939

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    I think Tesla's description of the slider helps keep it simple by encouraging owners to charge to a level that gives enough range for daily use while minimizing their average SOC.

    This confirms what we've already seen in battery degradation studies:

    http://www.nrel.gov/docs/fy12osti/53817.pdf
    http://www.cerdec.army.mil/directorates/docs/cpi/Cycled_Aged_LiIon_Cells.pdf

    The calendar life of Li-Ion batteries is shortened by spending long periods of time at high temperatures and high SOC, especially both in combination. Maintaining a low SOC can protect against the effects of high temperatures, and low temperatures can protect against high SOC (which is why Tesla aggressively chills the battery during a Range charge). The US Army study shows that cycling from 0% to 50% is better for battery life than cycling from 25% to 75%, especially in warm temperatures.

    The problem with recommending a "best" number is there is no one best number for everyone, only what's best for you based on how you drive your car. Range and battery health are mutually exclusive. The best setting for battery life is to keep the charge below 50%. The best setting for a >200 mile road trip is to charge to 100%. Only you know how much range you need on a daily basis. The slider gives you a tool to reduce battery degradation while still meeting your daily driving needs.

    Al, if your daily driving is less than 30 miles then you're best keeping the slider at 50% and bumping it up whenever you need more range. This is how I've been running my Roadster and I have zero capacity loss after three years.

    ImageUploadedByTapatalk1368998458.977042.jpg
    ImageUploadedByTapatalk1368998493.620543.jpg
     
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  3. bollar

    bollar Disgruntled Member

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    Thanks for posting the charging screenshots.
     
  4. vfx

    vfx Well-Known Member

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    Timed with Tesla saying that they will cover the battery if there is a problem. (of course not loss of range)


    attachment.php?attachmentid=22239&d=1368998438.jpg

    I would have put the "daily" bracketing at the far left of the green bar. Does it dynamically change on an adverage each day?
     
  5. kendallpb

    kendallpb Model S: P 8061

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    They recommend 50-90% but that looks like 50-70%. Like you, I wonder what this is--dynamic showing past usage/tailored recommendation, or what.

    It sounds like 90% (the new default max) and how they "decide" to stop charging may result in a lower charge; anyone with 4.5, what do you find after a 90% charge--same as the old Standard?

    IMHO a % is confusing when people think in terms of miles and Tesla talks in miles. "Math is hard!" ;-) Does 4.5 finally let you see the current charge as a %? (I don't see how to tell that now--it's all miles.) If not, that's a problem (telling people to pick a % but not telling them what % they're at or have used). I know how unscientific "miles" is for an EV, since it depends on so many factors like speed, driving style, etc.--but it's tough to get away from it since Richmond is 125 (actual) miles from my house, not "50% of a range charge" from my house. ;-)
     
  6. Trnsl8r

    Trnsl8r Blue 85kwh since 12/8/12

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    This. Try telling an ICE car owner how much gas he should keep in his car on any given day. I never know how many miles I might need. That slider will be on highest non-range setting when/if the update comes...

    Honestly, since I bought the car with 4.1, sleep mode disappeared and the google maps started staying in night mode when I back out of the garage. The only really useful upgrade so far was the scheduled charging. Think I'll be hitting the postpone button once a day once this rolls out.

    (end rant. sorry.)
     
  7. kendallpb

    kendallpb Model S: P 8061

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    This "set it to what you need" seems likely to increase range anxiety and/or lead to more running out of juice, I mean for average or at least non-TMC folks. It takes away some of the joyful simplicity of owning an EV, though I realize it's a practical recommendation. But after hearing "top off/always have a full tank in the morning" as a feature, now hearing "use a crystal ball and charge what you need" is a bit unsettling, especially if you have an unpredictable life. Mine's actually pretty predictable...weekdays. But I can't see trying to remember to reset this two days out of seven.

    It sounds like it's better for the battery, but Tesla isn't totally clear on that score--they say over 90% is worse, but also to charge only what you need, which implies that 90% is bad...maybe 85% is bad...how about 80%...when is it safe? ;-) I anticipate battery abuse and/or range anxiety, neither of which I want, plus sometimes "oh sorry, I can't drive--Tesla says to charge only what I need so my old 230ish range is now 115ish and I ran too many errands." This won't impress folks who might be interested in a Model S.

    Sorry to ramble. This just seems to me to make EVs more complicated and perhaps scare off some potential purchasers for whom a Model S would be perfect. Hopefully I'm wrong. The Model S is so straightforward; this feels like a step backwards to me. Maybe they should've just made a third category (Max, Standard, and below that, something around 70%) while still showing the slider for advance users. As they expand more and more to regular car drivers, IMHO they need something simpler than "predict what # between 50-90% will be enough." :cursing:

    The other 4.5 updates look great, though--especially the Supercharger list and using shore power when plugged in (I think).
     
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  8. Todd Burch

    Todd Burch Electron Pilot

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    You guys are all overthinking this. If you don't need or want the control, set it to 90% or whatever and don't fiddle with it. We're talking about a relatively small difference over the life of the pack.
     
  9. lolachampcar

    lolachampcar Active Member

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    and the default will likely be 90% when the SW is installed thus you only need to think about it when you need max range... kinda like it is today.
     
  10. dsm363

    dsm363 Roadster + Sig Model S

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    Your daily charge appears to be the same each day and would stay at the level you set it at.

    I agree people may be over thinking it. If you only drive 30 miles a day and can't ever see a need to drive more than 100 miles without a few hours notice they charge at 50%. If you need 30-120 miles I a day and can expect the occasional 200 mile trip with no warning then charge at 90% for the 85kWh pack.
     
  11. djp

    djp Roadster 2.0 VIN939

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    Agreed, this isn't a huge effect. If you keep the charge at 50% you'll probably see little to no capacity loss, compared to around 1% to 2% per year at 90%. Not a big deal if you're already planning to replace the battery or the car after 8 years.
     
  12. Andrew

    Andrew Model S #6151

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    I'm quite excited about this new option, for exactly this reason. I don't want to replace my battery if I don't have to, for both financial and environmental reasons. For 99% of our driving, we won't need more than a 50% charge. To be able to get that while extending battery life makes me a happy camper.

    Perhaps in the future they'll need to offer both settings methods. Default can be the "Basic Mode" (which includes the old Standard/Max toggle) and then an "Advanced Mode" (with the new % slider) that you can enable, just for us geeks.
     
  13. Trnsl8r

    Trnsl8r Blue 85kwh since 12/8/12

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    Not to disagree with you, but this is what a bunch of dudes (and gals) sitting around in an internet forum are speculating it might be. Official word from Tesla would go a long way for those of us "overthinking it".

    And to be fair, those on this side of the fence are harping mostly with prospective customers in mind, rather than ourselves. The simplicity and always having a "full tank" in the morning are some of the key selling points when converting ICE drivers, and some of that will go away with this. kendallpb's crystall ball comment above was spot on.

    - - - Updated - - -

    I like this idea.
     
  14. djp

    djp Roadster 2.0 VIN939

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    We have pretty good data from the US Army and industry studies on battery degradation, plus this forum's collective experience with the Roadster batteries, so I see the estimates more as an educated guess than pure speculation. :smile:

    It would be great if Li-Ion batteries never degraded and weren't affected by high temperatures or SOC, but unfortunately we can't fight the physics of battery chemistry. I prefer Tesla's approach of educating owners and giving them the ability to manage it, rather than sweeping capacity loss under a rug.

    EVs are different than ICE cars and capacity loss over time is part of the learning curve. It's better to have potential owners understand this up front rather than being surprised a few years down the road.

    For most people the capacity loss is low enough not to be an issue and they can set to 90% and forget it.
     
  15. apacheguy

    apacheguy Sig 255, VIN 320

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    Am I the only one that finds this odd? If this study is correct then why does Tesla hide the bottom 4 percent? Tesla has told us that cycling the battery to 0% will resulting in bricking and it is therefore not recommended (and indeed not possible in the Model S).
     
  16. dsm363

    dsm363 Roadster + Sig Model S

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    Bricking refers to the battery being permanently damaged. Going to zero may disable the car but plugging it in right away should save the pack. Going to zero and letting it sit there for months on end will destroy the pack at some point. Tesla likely hides some room at the bottom to allow the car to sit at zero miles for aping time before any permanent damage happens to the pack.
     
  17. derekt75

    derekt75 Member

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    agreed.
    Most of my days I'll drive fewer than 50 miles.
    The problem is that some of the long drive days are unpredictable. All of a sudden you find out that your friend can't use his center court tickets to a playoff basketball game, and you don't want to have to say, "gee I'd love to use them, but unfortunately my car won't get me there because I only charged to 50% last night".

    I'll gladly pay a mile or two of range a year for the peace of mind of knowing that on any day I can go anywhere I need to go.

    If that's not worth it to you, I guess it's great that they've got the new feature, but for me, the old way was simpler.
     
  18. dsm363

    dsm363 Roadster + Sig Model S

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    If you are willing to take a small hit on range a year, charge back up to the old standard charge and everything is back to the way it used to be. All this does is give people who want a little more control that option.
     
  19. Kaivball

    Kaivball Member

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    I hope I get your battery with battery swapping...

    :)
     
  20. Andrew

    Andrew Model S #6151

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    Ha! You'll be prying my battery out of my cold, dead hands... ;)
     

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