Battery bar drops next morning

Discussion in 'Gen 3 Prius Fuel Economy' started by evebill8, Feb 22, 2012.

  1. evebill8

    evebill8 Member

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    Hi folks,

    When I drive home after work, the battery always shows 7 bars. The next morning, it shows only 4 bars when I starts the car. Is it normal? What drew the battery power over the night? Thanks!
     
  2. fotomoto

    fotomoto Senior Member

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    I can't say it's normal in the sense that there's an explanation for it in the owners manual but you're not the first to notice it and ask.
     
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  3. macman408

    macman408 Electron Guidance Counselor

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    Sometimes it happens when I'm not paying attention to what the battery level is when I park, and I see it lower than I expected the next morning. :)

    But one reason why this can happen is the way that the car figures out and corrects errors in its SoC estimate. It counts coulombs in and out of the battery while it's running, since battery voltage will vary quite a bit with temperature, load, SoC, and many other variables. When it's off for a while, that gives the voltage time to settle to a level that is more directly indicative of the SoC only, so it can use that information to correct any errors accumulated through the previous calculations based on coulombs. That's my understanding, anyway.
     
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  4. 32kcolors

    32kcolors Senior Member

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    A few members have reported that but it's never happened to me. Maybe it has to do with the climate?
     
  5. qbee42

    qbee42 My other car is a boat

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    Macman has it right. The SoC display is only an estimate of the real SoC, as there is no way to directly measure SoC like you would fuel in the gas tank. The guesstimate at startup is based on cell voltage, where the running estimate also include charge counting. It's not unusual for them to differ.

    Another similar issue is a sudden drop in SoC after starting in the morning. This comes from a heavy reliance on the battery during the first few minutes of operation, which pulls down the SoC.

    Tom
     
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  6. h00ktern

    h00ktern Member

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    I've run Techstream a few times while driving to & from work (10 mi each way), much like a Scanguage. I noticed that the SOC appeared to update very much more quickly in TS, than the Battery meter would reflect; the Battery meter always seemed to lag. It was so apparent that I no longer trust the Battery meter to represent the actual SOC - more just a guide.

    I don't remember what the actual % of charge represented on the Battery meter. I seem to think it was only like a 20-30% SOC difference between one bar low of "full", to three bars remaining.

    Your case may be the reporting lag, equalization of the battery's SOC overnight, and a temperature change influence. The next boot-up reflects what it finds.
     
  7. Codyroo

    Codyroo Senior Member

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    Some great and informative answers given. Here's a question for evebill8 - describe the last 1 - 3 minutes of your drive home, prior to shutting the car down. If it is something like,

    25 mph speed limit
    EV Mode for last 0.75 miles

    It would support the scenario described by macman.
     
  8. evebill8

    evebill8 Member

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    Yes, it is pretty much like that. when I am about home, I do not run EV mode, but I just run 25 mph slow.
     
  9. macman408

    macman408 Electron Guidance Counselor

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    You might be seeing the hysteresis of the gauge, not necessarily any lag; basically, if you discharge the battery only until it loses a bar, you have to put several percent SoC back before the bar shows up again. This isn't so much lag as it is a feature to keep the bars from flickering, or changing too often. I haven't paid strong attention to it, but I think it updates basically instantly relative to what I'm getting from my ScanGauge.

    This post gives the SoC levels for various battery bars in the Gen II; it's similar for the Gen III.
     
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  10. h00ktern

    h00ktern Member

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    I'll look into it on my '11 and see if I can make something of it.
     
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