Maximizing battery health - Heat and State of Charge

Discussion in 'Prime Plug-in Charging' started by m8547, Jun 12, 2019.

  1. m8547

    m8547 Member

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    We know that both heat and leaving the battery fully charged can be detrimental to its health in the long run. And I know that fully charged is really only 82%-ish SOC, but it's still better for it to spend more time at lower SOC. So how should I adjust my charging habits to maximize the life of the battery?

    • Commute to work:
      • Option 1: plug in when I get to work
        • Pros:
          • Cooler weather while charging in the morning
        • Cons:
          • The battery is warm from driving and gets warmer as it charges
          • The car will sit in the sun the rest of the day, with the battery fully charged and slowly getting warmer
      • Option 2: Plug in in the afternoon
        • Pros:
          • Battery stays less fully charged during the day
          • I could set pre-conditioning to cool off the cabin before I leave
        • Cons:
          • Battery is warm from sitting in the sun at the start of charging, and continues to sit in the sun while charging (but maybe the traction battery cooler cycle will run?)
          • less convenient
    • Commute home:
      • Option 1: Plug in when I get home
        • Pros:
          • The battery is hot from being in the sun and from the drive home, so the traction battery cooler cycle will run to cool it off
          • More charge is available if I decide to do errands
        • Cons:
          • Traction battery cooler cycle uses a little more energy
          • The battery will sit fully charged until the next morning
      • Option 2: Set a charge timer to finish early in the morning
        • Pros:
          • The battery stays less fully charged during the evening
        • Cons:
          • The battery stays hot for a long time after the commute home

    I guess my questions are:
    • How much does charging heat up the battery for L1 or L2?
    • At work is it better to charge in the morning while the battery is a little cooler, or wait until the afternoon when it might be a little warmer?
    • How effective is the traction battery cooler cycle?
    • When I get home Is it bad to park when the battery is hot and let it charge later, or should I plug in right away and let it run the AC to cool itself off but also charge?
     
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  2. John321

    John321 Member

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    Another option is to just drive your car and enjoy it, plugging in whenever you are able and trusting the engineers who put this car together with the battery management system will know more about whats best than you or I ever will.
     
  3. hill

    hill High Fiber Member

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    Even driving my wife's plug-in Pacifica, I noticed on a day like yesterday when the temperatures were 103°, the battery coolant will get up to 110°. But charging in the morning (coolant fans come on) , with the programming set for departure time, the traction pack will be cooled down to 75° - as the morning outside temperature is around 68°.
    Just observations, on a liquid cooled plugin. With fans/air cooled - YMMV.
    .
     
  4. sam spade 2

    sam spade 2 Senior Member

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    GASP.
    What a novel idea.
    Which flies in the face of everything OCD !!
    :ROFLMAO:
     
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  5. m8547

    m8547 Member

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    Thankfully the engineers considered this problem and added a section to the owner's manual, since the driver has some control over the conditions the vehicle experiences. The thermal management for the battery in this car is limited, compared to a car with liquid cooling for the battery. If it had a better thermal management system it would probably be fine to just drive it and never have to think about it.

    upload_2019-6-12_13-14-11.png

    They specifically say that the rate at which the battery capacity declines will vary. I want my car to last a long time, and I use EV mode heavily (my commute is 30+ miles round trip, 100%the time in EV mode since I can charge at work, and more than 2/3 of my total driving is in EV mode). So I'm asking for advice to minimize battery degradation based on what the manual says and based on common knowledge of lithium batteries, since a few bullet points in the manual isn't enough to cover every possible scenario.

    There are some things I have no control over, such as the fact that it is hard to avoid "high temperature and direct sun" where I park and charge at work. But for example changing the time of day when I charge takes almost no effort.
     
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  6. Prius from Dad

    Prius from Dad Senior Member

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    Leaving a full battery in the hot sun is not good for the battery long term. Since you can't control the weather, I would use the charge timer (with climate prep on) at home and at work. This way the battery is at full charge for only a short while.
     
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  7. m8547

    m8547 Member

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    Is it bad to charge at the end of the day when the battery is hot from sitting in the sun all day? Charging generates heat (how much?), and the traction battery cooler won't run unless it's hot enough to ask at the beginning of the charging session.
     
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  8. Mendel Leisk

    Mendel Leisk Sidewalk Supervisor

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    If there's easily done measures that could improve the battery's life, I'm all for it, I mean: why not?
     
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  9. Prius from Dad

    Prius from Dad Senior Member

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    I think it is worse to leave a full battery sitting in the hot sun all day than to charge when it is hot out. If you have access to your car before the charging starts when it is hot out, just turn it on then off and the battery cooler message will show up. I don't know how much heat charging generates, some more knowledgeable members may be able to help with that.
     
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  10. m8547

    m8547 Member

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    I can only park at the chargers at work for up to 4 hours (preferably less if there's high demand so everyone has a chance to charge). So I have to move my car at some point during the day, whether I charge in the morning or afternoon.

    My only concern is that if the battery is not quite hot enough for the traction cooler message to come up when I start charging, could it get too hot charging while sitting in the afternoon sun? I don't think the cooler will run if it doesn't ask when you park, no matter how hot the battery gets. I think in some cases if it gets too hot it will slow down the charging speed, which is also not ideal if I am expecting it to charge in a certain amount of time. I saw signs of that on the old Chargepoint charger, but that one had "shared power" and seemed to have issues with the charging rate randomly being limited for no reason, so I couldn't tell when the car was limiting the charging rate vs when the charger was limiting it. The new Chargepoint chargers they put in don't have that problem and provide the full 6.6KW per outlet.

    So I think it comes down to how much heat charging generates, as you said. Maybe I'll buy an ODB reader and do some experiments.
     
  11. bisco

    bisco cookie crumbler

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    are you tinted to the legal maximum, and using solar window shades?
     
  12. m8547

    m8547 Member

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    I'm pretty sure we established in this other thread that tint doesn't do much for heat. I'd like to get it tinted but it's not worth the cost to me.
    Windows film expectations | PriusChat

    I use a sun shade in the front. I could use more but already the front is barely worth the time to put up. I'm not going to add a few minutes to my commute each day installing and removing sun shades. Plus I'd look kind of crazy. I do open the windows when there is low chance of rain.
     
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  13. hill

    hill High Fiber Member

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    It's really the Shaded asphalt you're sitting on. That can mean and easy 35° difference.
    .
     
  14. jb in NE

    jb in NE Senior Member

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    Option 2 for both. Charge the battery just before you want to use the capacity you put in it.

    Commute side - if the car is hot, the A/C will run as necessary, powered from external power. The battery will be protected.

    Home side - charge just before you need the power.
     
  15. sam spade 2

    sam spade 2 Senior Member

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    Charging the battery when it is REAL HOT probably is not good for it.
    You might want to limit your charging at work to the first couple of hours after you arrive.

    In the end, no matter what you do it is not likely to have any significant impact on the life of your battery.

    Are hybrid owners more prone to OCD than the population in general ? Sure seems like it. ;)
     
  16. hill

    hill High Fiber Member

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    heat from charging is a ratio how many KW's are going in, & the traction pack size. Since the prime only charges ~ 3½kW's - the incoming current isn't going to have a critical amount of heat added, but still, you wouldn't want to do that on 100° day sitting on hot black asphalt.
    .
     
  17. jb in NE

    jb in NE Senior Member

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    And on L1 it is a lot less.
     
  18. hill

    hill High Fiber Member

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    Yep - 2hrs L2 or 6hrs L1.
    .
     
  19. jb in NE

    jb in NE Senior Member

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    Here's what the Prime owner manual has to say about capacity reduction in the traction battery.

    The capacity of the hybrid battery (traction battery) will decline gradually when the hybrid battery (traction battery) is in use. The rate at which it declines will differ in accordance with environmental conditions and the way in which the vehicle is used. Observing the following can help suppress battery capacity decline.

    ●Avoid parking the vehicle in areas with a high temperature under direct sunlight when the hybrid battery (traction battery) is fully charged.
    ●Avoid accelerating and decelerating frequently and suddenly when EV driving.
    ●Avoid frequent driving near the top speed for EV driving.
    ●Leave a low level of charge in the hybrid battery (traction battery) when leaving the vehicle undriven for a long period of time. After confirming that EV mode has switched to HV mode, turn the power switch off.
    ●Use the charging timer function as much as possible in order to fully charge the hybrid battery (traction battery) immediately before starting off.

    From this we would conclude that it is not preferable to charge the battery on arrival to work and leave it in the hot sun the rest of the day with a full charge (1st and last paragraphs). Better to charge just prior to leaving to drive home. If the car is hot and the battery needs cooling, the HVAC system will provide it during charging. If you charge earlier in the day, there will be no cooling for the hot battery the rest of the day.

    For the same reason, at home use the charge timer and charge the battery just prior to leaving to drive to work.

    If this were the case, Toyota probably would have omitted that section of the owner manual.

    The car will run its HVAC system as required to cool the traction battery during charging. The subsequent paragraphs of the manual note that if it is very hot or very cold when charging, the battery will not charge fully to protect itself:

    When the remaining charge of the hybrid battery (traction battery) is low after charging

    In the following situations, the remaining charge of the hybrid battery (traction battery) after charging completes may be less than normal in order to protect the system (the EV driving range after the battery is fully charged may be shorter).*

    ●Charging is carried out when the outside temperature is low or high

    ●Charging is carried out immediately after high-load driving or in extreme heat

    If you charge in the afternoon and the car is not fully charged (and you don't suspect the problem you were having with the L2 charger), then it is likely that the termperature was too high for the battery to fully charge. You may also see this message on the MID:

    From Clipboard.jpg

    You will also want to ensure the charging equipment cooling air intake vents under the rear seats are not blocked and are kept clean.
     
    #19 jb in NE, Jun 13, 2019
    Last edited: Jun 13, 2019
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  20. sam spade 2

    sam spade 2 Senior Member

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    And my opinion is: If any of that really made any SIGNIFICANT difference to the longevity of the battery, they probably would have included a guestimate as to how much.

    What they are quoting is an engineers view of battery parameters.
    They, no doubt, put that same wording in the very first hybrid manual......without any real world data to know if it was going to be a factor or not. They may still not have any.
     
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