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Optimal charging level leaving Prius Prime parked for long periods

Discussion in 'Prime Main Forum (2017-2022)' started by BChoAss, Jun 18, 2022.

  1. BChoAss

    BChoAss Junior Member

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    I'm aware our owners manual states:

    Section 2-2:
    How many of you strictly abide by this? To be honest I had times where the battery was full for weeks at a time.
     
  2. schja01

    schja01 One of very few in Chicagoland

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    Still have never seen the definition of “long time “.
     
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  3. jerrymildred

    jerrymildred Senior Member

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    I think "weeks at a time" would qualify as "a long period of time."

    But it's not a binary question such as leaving it full for one week will ruin the battery but leaving it full for six days and 23 hours will do no harm. It's more of a "the more time it spends a max charge, the quicker the battery will degrade." The manual lets you decide how long you want to try to make it last. I never leave mine fully charged for more than a few hours.
     
    #3 jerrymildred, Jun 18, 2022
    Last edited: Jun 18, 2022
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  4. bisco

    bisco cookie crumbler

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    mine has never been left fully charged. 10 years old, 80,000 miles, 60 of which is ev.

    lost about 18% of range, idk if that's good or bad.
     
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  5. Washingtonian

    Washingtonian Senior Member

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    When I first got mine I didn't know that you shouldn't park it a long time fully charged. Once went on a 56 day cruise and charged it fully. Checked the HUD to see how many miles it would go on that charge. Then checked it again when I came home to see how much charge it had lost sitting for two months. Almost no difference; something like going from 27.2 miles to 27.1. Later I found from this forum that I shouldn't do that. I doubt that it makes a significant difference, though. After five years it still seems to hold a charge like when it was new.
     
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  6. bisco

    bisco cookie crumbler

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    they say the same thing about phones and computers, but the chargers keep them topped up all the time.
     
  7. Tideland Prius

    Tideland Prius Moderator of the North
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    I did when I had the car. Any time I was on vacation, I’d arrive home the day before departure in HV mode.
     
  8. Gokhan

    Gokhan Senior Member

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    This translates as the optimal charging level being 0% (--) SOC (SOC for EV-only driving) according to the second sentence—as the HV mode is switched into when SOC is 0% (--).

    This means that it is best to charge the battery immediately before driving and leave it uncharged at all other times, even when undriven for shorter periods.
     
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  9. fotomoto

    fotomoto Senior Member

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    The rule of thumb that I've seen for leaving a LiOn battery for long duration is currently (pun not intended) about 40% charge.

    • Lithium-ion must be stored in a charged state, ideally at 40 percent. This prevents the battery from dropping below 2.50V/cell, triggering sleep mode.
    BU-702: How to Store Batteries - Battery University.
     
  10. Gokhan

    Gokhan Senior Member

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    You're forgetting that the SOC shown on MFD isn't the overall SOC. There is a forbidden buffer and the HV reserve. 0% SOC on MFD may correspond to 30–40% overall SOC.
     
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  11. jerrymildred

    jerrymildred Senior Member

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    Actually, from @john1701a's excellent videos, we can see that 0 miles left is roughly 14% SOC. (Bottom picture showing 0.6 miles left at 15% actual SOC.) At 40% actual SOC, the display shows about 36%, so to keep it near 40% actual, you'd want to leave it at 36% displayed, but 40% on the display is close enough if you like round numbers.


    Screen Shot 2022-06-19 at 12.10.09 PM Large.jpeg

    Screen Shot 2022-06-19 at 12.10.36 PM Large.jpeg

    Screen Shot 2022-06-19 at 12.12.23 PM Large.jpeg

    So, leaving it with no EV range is much lower than some suggest for long term sitting.
     
  12. bisco

    bisco cookie crumbler

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    are all lithium batteries and bms created equal?
     
  13. fuzzy1

    fuzzy1 Senior Member

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    Isn't there also a buffer on the top side?
    My current laptop and phone have configurable charging strategies meant to improve battery longevity. E.g. I was able to set my laptop to charge to only 80% when ordinarily plugged in. And my phone remembers my patterns, and looks at the morning alarm setting, and initially charges really slowly, ramping up to faster charging closer to wake-up time. I've awoken a half hour before the alarm to find the phone still not fully charged. But with its bigger battery and better energy management, it doesn't matter that it isn't full, as it takes several days for me to draw it down from 90% to 50%.
     
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  14. bisco

    bisco cookie crumbler

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    wonderful! please share models for my next upgrade
     
  15. fuzzy1

    fuzzy1 Senior Member

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    You might not need to wait, it might already be on your machine, or available as an app from the manufacturer. This article describes several brands:

    How to Extend Your Windows Laptop's Battery Lifespan With a Battery Charge Threshold
    Setting a battery charge threshold can be as easy as downloading an app and setting the right options, and doing so can extend your battery's life.

    My Dell is 2.5 years old, though I only recently discovered this feature, under "Settings" here:

    upload_2022-6-19_13-36-45.png

    For the phone, I recently moved to a Moto G Power on Android 11. These Moto phones should be on the budget trailing edge, so better phones should have had it earlier. Though maybe the feature is tied to the Android version, two steps up from my old one. Go to Settings | Battery, then scroll down and explore the menus under Adaptive Battery, Optimized Charging, and Overcharge Protection.
     
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  16. bisco

    bisco cookie crumbler

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    thanks, i have an old mac book and i phone. i have considered moving back to windows in the future, and maybe android. i'll see what each has to offer when the time comes.
     
  17. Gokhan

    Gokhan Senior Member

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    So, I guess the analog battery SOC indicator on the MFD is not a true indicator. If it were true, the HV capacity would be about 34% of the overall capacity.

    It is true that every lithium-ion battery is different—they like different charging states for longer life, depending on the particular design.

    I don't think the lower forbidden buffer is known. It could be quite large, as Toyota plays safe. So, when you say 14% SOC, I'm sure it's at least about 25% absolute SOC for a 100% depth of discharge.
     
  18. Salamander_King

    Salamander_King Senior Member

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    We have discussed this in a different thread. So I am not going to repeat my bases, but all the data presented by others and known specs of the PP indicate that PP's traction battery has an upper buffer of ~16% and a lower buffer of ~14%. This lower 14% includes the HV portion of the battery. So, unless you have some data to share with us to point to a bigger lower buffer, I believe ~14% absolute SOC is at the point when EV range depletes and switch to HV, which is what Toyota suggests to keep the traction battery for a "long time" storage.
     
    #18 Salamander_King, Jun 19, 2022
    Last edited: Jun 19, 2022
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  19. Gokhan

    Gokhan Senior Member

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    I wouldn't be so sure about that. 14% × 8.8 kWh = 1.2 kWh, which is smaller than the non-plug-in battery and leaves no space for a protective buffer. Remember that since the protective buffer must be in a certain percentage (5–10%?), it will increase with the battery size.
     
  20. Salamander_King

    Salamander_King Senior Member

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    A regular Gen 4 uses either 0.75-kwh lithium-ion batteries or a 1.2 kwh nickel-metal hydride. So, 1.2 kWh is big enough to cover the entire HV portion plus 0.45kWh.

    From the published spec of 133 MPGe = 3.946002 mi/kWh and 25miles of EV range, we know that the Toyota has allocated ~6.3kWh of the traction battery for the EV operation. 6.3kWh/8.8kWh= 0.719946551168 meaning ~72% is used for the EV operation. This leaves approximately 28% of the traction battery SOC outside of the EV operation which is very close to observed data of 16% top buffer + 14% bottom buffer.

    Here is the copy of the explanation for the upper and lower battery SOC buffer I have given in another thread.

    As you can see below, the 100% SOC on MID is actually 80-85% and --% on MID when EV range is depleted is somewhere around 10-15% real SOC. Anything below this lower threshold is used strictly by the HV mode. During the HV mode, the real SOC can dip as low as ~7%, but that is rare. Thus it was concluded that the top reserve is ~15% and the bottom reserve is ~10%, leaving ~75% total of usable portion for the operation (this includes both EV and HV portion). Still, the question remains where the precise EV/HV transition occurs. If you take the single point data from the graph below as one example, then it is at ~15% SOC, but I think this number varies somewhat by other factors.

    [​IMG]
     
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