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Would a 2009 need a new 12v battery?

Discussion in 'Gen 2 Prius Fuel Economy' started by jcgee88, Feb 25, 2010.

  1. jcgee88

    jcgee88 Member

    Joined:
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    Location:
    Maryland Heights, MO
    Vehicle:
    2009 Prius
    Model:
    N/A
    I have seen the various threads that suggest that
    a weakened 12v battery can result in lower mileage, by
    causing the ICE to turn on more than necessary to
    charge that battery.

    I bought a low mileage 2009 at the beginning of
    February, and have experienced MPG that is on
    the low side of the normal range. I do intermixed
    city and freeway driving. I had been getting 43 MPG
    according to the MFD, then discovered the trick
    about inflating the tires to 42/40 psi, and now
    my overall is 43.1 MPG over my initial 160 miles.

    One thing that leads me to suspect that the
    battery is weak is that when I first power on the
    car, it almost always starts the ICE within 10-20
    seconds. In other words, even the low speed moving
    the car from a parking spot, which I sense should be
    in stealth mode, is being powered by the ICE.

    I have since tested the battery using the
    "Vehicle Signal Check" process from jdenenberg:

    Unloaded battery: 12.1v (supposed to be 12.4 to 12.8)
    Under load: 11.9v (supposed to >12v)
    Charging: 14.1v (supposed to be >13.6 and <14.4)

    These results were after the car had sat unused
    for three days. The first two measurements are
    low, the third is in the acceptable range.

    Since this is a 2009 model, I find it hard to believe I
    would need a new 12v battery. But, the measurements
    would seem to indicate that I do. And, maybe the
    car's low mileage indicates that it sat unused (which
    is usually not good for a battery) much of the time.

    Any opinions or advice?

    John
     
    #1 jcgee88, Feb 25, 2010
  2. firepa63

    firepa63 Former Prius Owner

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    The ICE will always come on after getting in the READY mode when the car is cold or has been sitting for a while. It's to warm the ICE for emissions control and to provide cabin heat in cold weather. What you are experiencing is perfectly normal.
     
    #2 firepa63, Feb 25, 2010
    1 person likes this.
  3. ksstathead

    ksstathead Active Member

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    Vehicle:
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    I would test the battery when it has rested overnight, rather than after 3 days.

    firepa63 is correct, the gen2 prius will light the ICE a few seconds after Ready Mode as part of its warmup (the gen3 will skip it if engine coolant temp >60C).

    For details on the warmup process, see the links in my spreadsheet here:
    http://priuschat.com/forums/knowled...perating-mode-availability-reference-aid.html

    Keep an eye on the battery, but I think you are likely fine, just need to read on P&G, etc and get some seat time with it. 50+ will come with warmer temps and more experience.

    Good luck!
     
    #3 ksstathead, Feb 25, 2010
    1 person likes this.
  4. Bob64

    Bob64 Sapphire of the Blue Sky

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    Your symptoms arn't caused by a low battery. The prius ALWAYS starts the engine when you turn it on from a cold start. It will then warm up the catalytic converter to minimum operating temp, and then shut off.
     
    #4 Bob64, Feb 25, 2010
  5. BAllanJ

    BAllanJ Active Member

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    Location:
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    You're probably experiencing lower than expected mileage due to low temperatures, winter gas and short trips. Summer should fix the first 2, and a nice driving holiday will fix the last one.

    and Welcome.
     
    #5 BAllanJ, Feb 25, 2010
  6. JimN

    JimN Let the games begin!

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    John, register your car at http://www.toyotaownersonline.com/index.html to see its service history.
     
    #6 JimN, Feb 25, 2010
  7. LRKingII

    LRKingII New Member

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    It's also possible that previous owner ran the battery down several times. It is a small battery and a couple of complete discharges will shorten it's life.
     
    #7 LRKingII, Feb 25, 2010
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Hi John,

    If you have access to a battery charger, then I'd suggest you try to fully charge the battery using the 2A setting overnight. See if that makes a difference to the voltage readings when you've let several hours elapse after removing the charger.

    Also, what constitutes low mileage?
     
    #8 Patrick Wong, Feb 25, 2010
  9. vertex

    vertex Active Member

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    In the North east in the winter time, 43 MPG is normal. You should get about 47 in the spring and summer.
     
    #9 vertex, Feb 25, 2010
  10. richard schumacher

    richard schumacher shortbus driver

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    Sounds normal for conditions. MPGs will improve as the weather warms.
     
    #10 richard schumacher, Feb 26, 2010
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