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12V battery charging

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by lpf, Jun 1, 2020.

  1. lpf

    lpf Member

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    Does conservative way of driving affect the 12V battery charging? I see that my battery gives around 11.8-12.0V in acc, 14.2V when in Ready, when I drive to work slower (25km away) . When I drive faster, the numbers are 12-12.3 and 14.4V. Battery is 18 months old, it's a normal battery fitted by the previous owner. I don't have any sign of difficulty to get the car ready. Actually I have no idea how the battery is charged and I will appreciate any info about it.

    Also I have to ask this: when I turn on the head lights, the dashboard instruments get dimmed, is that normal?
     
  2. davecook89t

    davecook89t Senior Member

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    Are you sure the Instrument Panel Light Control Dial is turned up to maximum brightness? It will turn easily until it is almost at the top. At that point, there is tactile resistance until the dial seems to click into its maximum brightness position. After first getting our Gen 2, I thought I had dialed up the maximum brightness, but had not turned the dial until I felt the click, being a little scared of breaking something. I believe others have had the same experience. Instrument Panel Light Control Dial.JPG
     
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  3. lpf

    lpf Member

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    I'm in Europe so I have a button with 3 settings: low, medium and full. The dimming happens in any setting when I turn the headlights on.

    Posted via the PriusChat mobile app.
     
  4. jzchen

    jzchen Newbie!

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    On our US v yes the dash lights dim when headlights are turned on. That is normal. It's kind of bright at night without that. There is a way to bypass this function as noted...

    moto g(7) power ?
     
  5. lpf

    lpf Member

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    Thanks. So my battery may be ok! If you know how to override could you please tell?

    Posted via the PriusChat mobile app.
     
  6. MickyMatter

    MickyMatter Active Member

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    That's normal behavior. It's kind of: "You need headlight? Then it must be dark outside. I'll dim the instruments for you."
    If you use the headlight at daytime, just press the button once (short) after switching on the headlight and the there's no dimming until next time using headlights.

    SM-G950F ?
     
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  7. lpf

    lpf Member

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    I'll try that tomorrow, danke!

    Posted via a Xiaomi mobile & the PriusChat mobile app.
     
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  8. RobertK

    RobertK Member

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    From what I've read here, a voltage of 14.2v while in Ready mode indicates a low 12v battery. My Prius shows 13.8v when the 12v battery is fully charged, either from driving or using a battery charger. The 12v battery is charged at a constant rate by the inverter whenever the car is Ready, and the 12v demands of the car are met by the inverter as well when the car is Ready. The speed you drive should not make any difference in the 12v charging rate.
     
  9. lpf

    lpf Member

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    Do you suggest to replace the battery or to charge it with a tender or something like that?

    Posted via a Xiaomi mobile & the PriusChat mobile app.
     
  10. jzchen

    jzchen Newbie!

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    As far as I know 13.0 V to 15.0 V is normal output of the DC-DC converter.

    See second post. That knob if you roll upwards until past a resistance is the disable. As a warning you may feel irritated at night time, but just push back downwards...

    moto g(7) power ?
     
  11. sam spade 2

    sam spade 2 Senior Member

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    WHAT ? Read what you posted again. NOT true at all.
    The voltage you read in READY mode is the charging voltage and has little to do with the actual battery.

    BUT....those other voltages he posted might not be good.
    Anything below about 12.3 in ACC mode might indicate a problem.
    I would worry about anything below 12.0.
     
  12. SFO

    SFO Senior Member

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    How many hours per day/week do you drive the vehicle?

    If you don't have a AGM compatible tender the with appropriate amperage, you can leave it in 'ready' which will charge the 12v as well.
     
  13. bisco

    bisco cookie crumbler

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    how old is the battery?
     
  14. SFO

    SFO Senior Member

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  15. bisco

    bisco cookie crumbler

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    yeah, that's definitely low for an 18 month old battery
     
  16. dolj

    dolj Senior Member

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    That would be a good idea, especially if the battery's voltage measures 11.6 V or less when the car is off (and has been off for 2 hours or more).
     
    #16 dolj, Jun 2, 2020
    Last edited: Jun 2, 2020
  17. lpf

    lpf Member

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    Around 15 hours usually. You suggest to leave the car in ready for 5-6 hours, during night?
     
  18. dolj

    dolj Senior Member

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    15 hours driving a day should keep the 12 V charged. If the battery shows low voltage (11.6 V or less) after sitting overnight, then it would suggest the battery needs to be replaced.
     
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  19. jzchen

    jzchen Newbie!

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    Oops. This is different. My apologies!

    moto g(7) power ?
     
  20. lpf

    lpf Member

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    No problem! Do you know that Arcadia is an area in Greece, one of the oldest civilized sites on earth?
     
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