Faster Charging Might be Better for the Battery (in a way)

Discussion in 'Prime Main Forum (2017-Current)' started by m8547, May 10, 2020.

  1. m8547

    m8547 Senior Member

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    This thread isn't to debate on the effect of charge current on the battery. That has already been discussed elsewhere.

    Instead, I had a thought about faster charging. Now that I'm staying at home and not driving everyday, the Prime's battery is spending more time fully charged, which is not the best thing for it. The problem is, it takes so long to charge on L1 that I usually let it charge overnight if I've gone anywhere in a day (I set a 7am departure time), just in case I might want to go somewhere the next day.

    But if I had a faster charger, there's a higher chance I could decide 2.5 hours ahead of time that I want to go somewhere, instead of deciding 5.5 hours ahead of time. So I could leave the battery mostly discharged until I'm ready to use it. My understanding is, the less time it spends fully charged, the better. And I'm aware it only actually charges to 85%, but less is better if it's going to sit for "a long time", whatever that is.

    Unfortunately my garage still only has a single 120V 15A circuit.
     
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  2. john1701a

    john1701a Prius Guru

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    Keep in mind that you don't necessarily need to fully replenish the entire charge to run an errand. Also, the charging itself is non-linear. That means you get more electricity initially, then it tappers down to a slow rate as the level reaches "full".

    In other words, for me to drive to town for something, it only takes 20 minutes of charging with my JuiceBox to cover the round-trip. That means very little planning ahead is needed. I just plug in when the idea of making a run comes up and it charges while I get ready.
     
    #2 john1701a, May 10, 2020
    Last edited: May 11, 2020
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  3. Salamander_King

    Salamander_King Senior Member

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    I have been keeping the car with 35-45% SOC (on the dash) which takes just about 2 hours to charge with an L1. At the current gas price in our region, EV is about 1.8x more expensive to drive, so I use HV mixed with EV on a day I have to do drive. I do a single ~50 miles a round trip weekly now. At this rate, a full tank of gas with a partially charged traction battery will last 4~5 months.
     
  4. schja01

    schja01 One of very few in Chicagoland

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    OP Why is this even an issue? Sine when the dash says the battery is 100% it really is at 80ish%. ??
     
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  5. m8547

    m8547 Senior Member

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    It's definitely not a big deal to occasionally leave it fully charged for a week. But we don't yet know the long term effect of driving it only once a week for a whole year or more, and leaving if fully charged in between, for example. Presumably that would be worse for the battery than driving it once a week and leaving it mostly discharged for the rest of the time.

    Not really a big issue, just something I think about when I'm bored and stuck at home.
     
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  6. m8547

    m8547 Senior Member

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    Around town is easy to manage, but some of my trips are still close to or longer than the range. For example if I go to Lowe's or Costco, they are both over the hill, and I think the round trip takes around 70% of the charge. I went to a drive-thru farmers market on Saturday, and that was 24 miles round-trip, and it used 89% of the available charge. I've stopped by work twice on the weekends to pick up some stuff, and that's 30 miles round-trip. I need to go to the garden center this week to ask about me dead tree, and that's 17 miles round-trip with some big hills.
     
  7. bisco

    bisco cookie crumbler

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    agree that L2 is a big help in certain situations. i never leave the battery fully charged for long periods of time, even though it's 80%, toyota recommends against it.

    i keep a 40-50% charge most of the time, and 20-30 minutes of L2 usually gets me where i want to go
     
  8. jerrymildred

    jerrymildred Senior Member

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    Same here. The other day, we decided to grab some take-out for supper. I had used up the EV the day before. So I just plugged it in for about 20 minutes on L2 and when I got back home it still showed 7 miles left. I guess I charged more than I needed but that's better than having the engine come on just as I pull into the driveway.
     
  9. Tideland Prius

    Tideland Prius Moderator of the North
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    Same. The light traffic allowed me to set a new record in efficiency - 9.0kWh/100km or 6.94 miles/kWh.

    To put that in perspective, I nearly matched the ridiculously optimistic JC08 (Japanese) test cycle of 8.18kWh/100km or 7.64 miles/kWh.
     
    #9 Tideland Prius, May 11, 2020
    Last edited: May 12, 2020
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  10. Washingtonian

    Washingtonian Active Member

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    I look at it this way. While the battery will probably last longer if we pay careful attention to only charge it just before we use it, and not to fully charge it if we know we are going to drive just a few miles, we don't know how much longer it will last. I would guess maybe 10 to 20 % longer. Since it is warranted for 150K miles in California, I expect that might be the minimum battery life if someone just "just drives it". I just did the math and at the rate I drive my car, I will be 102 years old when the car reaches 100K miles. So babying the traction battery is not a high priority for me.
     
  11. mr88cet

    mr88cet Senior Member

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    In our case, thankfully, our laundry room is on the opposite side of a common wall with our garage. Since we use a gas dryer, it was pretty easy to get an electrician to flip the 240V outlet for the dryer to the other side of that wall.

    BTW, typically Li-ion batteries “prefer” to be stored at around 1/2 to 2/3 charged (thereabouts). The ideal level depends upon the particular battery chemistry.

    Also in my BTW and FWIW cabinet: In my particular case, during the shelter-in-place time, our usable battery capacity has plummeted to about 22 miles, both on the all-knowing Toyota guesstimatron (GoM) and in reality. The actual, physical battery capacity has almost certainly not changed that suddenly; I’m pretty sure the computer is just confused/panicking over the sudden change, and has increased the charging margins. Driving range has swung low and recovered later before, although not this low before.
     
    #11 mr88cet, May 12, 2020
    Last edited: May 12, 2020
  12. john1701a

    john1701a Prius Guru

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    There is no margin change, an aftermarket gauge will confirm. Living in Texas, you simply don't get to observe the routine swings we see from there extremes in the north. Here in Minnesota, we witness those changes as Spring throws us a stay-at-home event which abruptly alters the usual Winter adjustment. The result is the impression of confused/panicking.
     
    #12 john1701a, May 12, 2020
    Last edited: May 12, 2020
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  13. bisco

    bisco cookie crumbler

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    not arguing, but it's more about loss of capacity (not covered by warranty) than it is about complete failure.

    folks around here freak out if they lose a mile of range :p
     
  14. CharlesH

    CharlesH CA HOV Decal #5 on former PiP

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    I got the impression that from Toyota's point of view, if the battery pack has enough capacity to operate the Prime in HV mode with zero EV miles (in other words, as a non-plugin Prius), then it has not failed, and there is no warranty issue.
     
  15. mr88cet

    mr88cet Senior Member

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    OK, what sort of gauge, and how do you know that the charging margins don’t change?

    I’ve definitely seen it’s EV range (actual and GoM, which have tracked all-in-all reasonably well) go from:
    * ~34miles initially,
    * then about 9ish months after I bought it, it went down in in three distinct steps, each a couple weeks or so apart, first to ~29, then ~27, then ~25.
    * it stayed at ~25 for a year or thereabouts.
    * it then rise back up to ~28 for a little over a year.
    * then recently, with the shelter-at-home order, it dropped down to 22miles.

    I can confirm that the number of KWh charged into the battery has varied proportionally with the EV range. It is actually charging different amounts into the battery, and that my miles/KWh has stayed pretty much the same throughout at ~4.6 miles/KWh.
     
  16. john1701a

    john1701a Prius Guru

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    Huh? Not sure how you could have possibly missed seeing so many of the videos posted. There's one below to ponder...

    That's perfectly normal, the same variation much discussed with regard to temperature. When it gets colder, the chemistry becomes less efficient, it takes more energy to recharge & maintain, and the driving itself requires more energy.

     
  17. mr88cet

    mr88cet Senior Member

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    Yes, I’ve seen some of those videos.

    So, here in Austin TX, June-September the daily temperature range is averages about 80 low to 95 high. In August, the highs are frequently over 100. December-February averages 40 low to 60 high, or thereabouts. I don’t think the temperatures ever get low enough to make much difference to the battery chemistry.

    We bought our ‘Prime in May of 2017. It was charging ~6.3KWh from the EV-HV threshold to the “100%” top margin. The first time the range dropped was in November or so, best I can recall. When it had dropped to 25 miles in the GoM (which again, for my use case, is reasonably accurate) it was charging about 4 1/2 KWh into the battery from “0” to “100%.” In short it was not particularly cold, even for Austin, in that time frame.

    Then, for about a year, the range went back up to 27-29 miles per charge, during which time it charged, typically, around 5.8KWh from “0” to “100%.”

    And now, when it’s plummeted to 22 miles (I don’t have a reading, but perhaps 4.1ish KWh being charged), again happened while temperatures have been in the 65 to 80ish range.

    So no particularly obvious sign of temperature affecting battery chemistry. I really doubt if any of the could realistically be accounts for by the physical battery cells changing. It seems far more likely that the computer is reacting to driving and charging conditions.
     
    #17 mr88cet, May 12, 2020
    Last edited: May 13, 2020
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