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2 Questions about Aux Battery voltage

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by dorf, Aug 9, 2016.

  1. dorf

    dorf Member

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    1. What is the optimum 12 volt aux battery voltage range
    2. Why does 12 volt battery voltage effect MPG
     
    #1 dorf, Aug 9, 2016
  2. andrewclaus

    andrewclaus Active Member

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    A new battery should read around 12.8V with no load, and should stay above 12V under accessory load.

    An old battery will take energy (in the Prius' case from the inverter) to try to maintain voltage, energy that normally moves the car.
     
    #2 andrewclaus, Aug 9, 2016
  3. dorf

    dorf Member

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    Thanks for the quick reply.
    I recently replaced the aux battery with a Optima Yellow Top....MPG was 51.2 after about a 100 miles or so , on hilly terrain and battery voltage after sitting over night was 12.86
    Previous MPG was 47-49 on basically the same roads
    Thanks again......from Arkansas
     
    #3 dorf, Aug 9, 2016
  4. fotomoto

    fotomoto Senior Member

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    In a HEV design, all energy comes from gasoline. The 12v is charged by the ICE spinning the generator. If the battery is weak, then more and more gas is needed to try and keep it topped off. Kinda' like leaving your a/c on all the time; an unnecessary drain.

    The same process holds true for the main HV battery. If it's weak, your mileage will go down.
     
    #4 fotomoto, Aug 9, 2016
  5. andrewclaus

    andrewclaus Active Member

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    A 2 mpg increase is fairly common after replacing an old 12V, I hear.
     
    #5 andrewclaus, Aug 9, 2016
  6. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    That sounds good. My Optima, installed last September, seems to hang out around 12.6~12.7. The car is not driven daily, maybe every second day on average.
     
    #6 Mendel Leisk, Aug 9, 2016
  7. dorf

    dorf Member

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    Thanks for the info
     
    #7 dorf, Aug 9, 2016
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