1. Attachments are working again! Check out this thread for more details and to report any other bugs.

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

    Joined:
    May 21, 2007
    132
    4
    0
    Location:
    Little Rock
    Vehicle:
    2007 Prius
    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

    Joined:
    Sep 15, 2009
    993
    324
    0
    Location:
    Golden, CO
    Vehicle:
    2007 Prius
    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

    Joined:
    May 21, 2007
    132
    4
    0
    Location:
    Little Rock
    Vehicle:
    2007 Prius
    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

    Joined:
    Apr 22, 2009
    5,602
    3,781
    0
    Location:
    So. Texas
    Vehicle:
    Other Hybrid
    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

    Joined:
    Sep 15, 2009
    993
    324
    0
    Location:
    Golden, CO
    Vehicle:
    2007 Prius
    A 2 mpg increase is fairly common after replacing an old 12V, I hear.
     
    #5 andrewclaus, Aug 9, 2016
  6. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    55,846
    38,875
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    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

    Joined:
    May 21, 2007
    132
    4
    0
    Location:
    Little Rock
    Vehicle:
    2007 Prius
    Thanks for the info
     
    #7 dorf, Aug 9, 2016
(You must log in or sign up to post here.)