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Sure Sign of Weak Battery

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Extronic, Jan 21, 2014.

  1. Extronic

    Extronic New Member

    Joined:
    Feb 4, 2013
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    Vehicle:
    2005 Prius
    I have a 2004 prius with 160k all original. 12V battery is 4 months old. I purchased it about 4 months ago. This is my 3rd 2nd gen prius. The first one had a similar issue. 2nd one with 192k miles was fine but sold it because of high mileage.

    I noticed the SOC varies a lot and changes quickly ( blue bars to full green on mfd). I plugged in my scangauge2 and took notes on the SOC. On freeways going 60-80mph the SOC stays between 60-65% but when I get off of the freeway off ramp, the SOC quickly raises to about 75%. I understand braking will charge the battery quicker but a 10% jump in a 80 yard off ramp seem like a lot.

    I also noticed simply braking at a stop light from 35mph will quickly charge 3%.

    Is this a sign of a weak battery?
     
    #1 Extronic, Jan 21, 2014
  2. nh7o

    nh7o Off grid since 1980

    Joined:
    Dec 10, 2011
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    Location:
    Hawaii
    Vehicle:
    2009 Prius
    Model:
    II
    With 160K miles, it is likely the battery is weak. Quite a wide range of lifetimes in the reports, now that GenII are getting older. Some go longer, some less. However, with no DTC being set, and no driveability issues (racing engine, sluggish, battery fan blowing audibly) then there is nothing to be done about it. Try to keep it cool back there by cleaning the fan, and no worries.
     
    #2 nh7o, Jan 22, 2014
  3. uart

    uart Senior Member

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    Location:
    Australia
    Vehicle:
    2005 Prius
    Yes I believe the amp hour capacity of many of our traction batteries will be in decline. I started noticing mine going that way before 100k miles. I try to compensate for it as much as I can. The biggest tips I'd give you are :

    1. To let the engine warm for 1 minute (on cold starts) before driving.

    And

    2. To use "B" mode for large descents, anywhere that you're likely to exceed 7 bars.

    Decelerating from 80 MPH can generate a bit of energy, and even for a battery with near new capacity 10% is only 120 Watt hours. Say you drop from 80 MPH to 35 MPH and capture 50% of that kinetic energy, that actually is about 120 watt-hrs right there.

    Example Calculation
    m=1700 kg (curb weight + 150 kg)
    v1 = 80*1.6/3.6 m/s
    v2 = 35*1.6/3.6 m/s
    E = 0.5 * 0.5 * m(v1^2 - v2^2) = 434 kJ (at 50% recovered energy)
    E = 0.5 * 0.5 * m(v1^2 - v2^2) / 3600 = 121 Watt hours.
     
    #3 uart, Jan 22, 2014
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