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New owner question - can I leave the car unplugged to drain the battery?

Discussion in 'Model S: Battery & Charging' started by Panoz, Sep 30, 2015.

  1. Panoz

    Panoz Member

    Nov 19, 2013
    Colorado Springs, CO
    I'm a new owner, not even a week old, and drive very little so far. I'm wondering of it would be good to discharge the battery down to 10% or some low number, then charge it back up. Given my schedule, the only way to do that is to let vampire drain and city driving consume the energy over a week or two, then charge.

    My car sits in a heated, insulated garage so there's not cold weather impact on the vehicle. Can I *not* plug in overnight for a while to discharge it once?
  2. stevezzzz

    stevezzzz R;SigS;P85D;SigX;S90D;XP100D;3LR

    Nov 13, 2009
    You can do that, of course; the question is why would you want to? Tesla's battery management systems are second to none, and the factory's official recommendation is to leave the car plugged in. Most owners plug in every night and charge to 80-90% unless they anticipate needing the extra range.

    There is one reason to occasionally allow the SOC (state of charge) to get down to 10% or so and then charge to 100%, and that is to allow the algorithms to get a better idea of the battery pack's actual capacity and thus give you a more accurate Rated range. Just don't leave the battery sitting at 100% for any length of time, if you can help it.
  3. JohnQ

    JohnQ Active Member

    Jan 1, 2012
    Redding, CT
    I'd echo Steve's comment. But, if you really want to discharge the battery, turn the heater on full blast. Will accelerate the discharge.
  4. Spit

    Spit Member

    Sep 18, 2015
    Yorkshire, UK
    Can you plug your Tesla in when you get home from work and set it to charge 1am to 4am each day to 90% and it cuts off at 90% or cuts off at 4am whatever is first?
  5. tomas

    tomas Only partially psycho

    Oct 22, 2012
    Ideal average SOC for battery life is ~50%. So if you drive short distances and want to optimize, you could charge to 60% nightly rather than 80+ and run down to 20% over week. Problem is rated range calculation wanders after a while and owners freak out. To keep that algorithm stable, you have to charge frequently to 90+ and occasionally discharge to 20-

    decide if if your main concern is battery health or mental health.
  6. LetsGoFast

    LetsGoFast Active Member

    Oct 13, 2014
    From a battery health perspective, the battery is happiest near the middle of its charging range. From the perspective of calibrating the pack's capacity to the displayed range, it is probably useful to occassionally perform a full charge although I'm not sure it is particularly important to do so from a fully discharged state.

    Really, I think these are all in the catagory of splitting hairs. If you avoid staying near 100%, you can probably ignore the whole issue completely and suffer no ill effects at all.
  7. brec

    brec Member

    Aug 3, 2015
    Las Vegas, NV
    You can specify a SOC percentage cutoff and a start time, but not a stop time nor duration.
  8. Tabarnouche

    Tabarnouche Member

    Aug 26, 2014
    Maplewood, NJ
    Call me crazy, but I would suggest you refer to the car manual. It is often filled with useful information. Here's some passages that I found interesting (especially the parts that I put in bold):

    "Model S has one of the most sophisticated battery systems in the world. The most important way to preserve the Battery is to LEAVE YOUR MODEL S PLUGGED IN when you are not using it. This is particularly important if you are not planning to drive Model S for several weeks. When plugged in, Model S wakes up when needed to automatically maintain a charge level that maximizes the lifetime of the Battery.There is no advantage to waiting until the Battery’s level is low before charging. In fact,the Battery performs best when charged regularly."
  9. Electric700

    Electric700 Active Member

    May 21, 2013
    Florida, United States
    Good points, it's better to charge to 50% or 60% for battery health, and just keep the car set to that level and don't worry about the rated range indicator, then charge to 100% once a year for battery balancing but immediately drive it after charging is complete. They might have optimized the software for the rated range display, because I normally charge close to 60% and don't have the rated range wandering issue.

    Also, I think it's better to let it discharge to 40% before charging again, and leave it plugged in as Tabarnouche indicated. It probably won't hurt if you need to leave it unplugged for one or two days though.

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