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Question about rear 12V battery.

Discussion in 'Gen 2 Prius Main Forum' started by Kablooie, Aug 31, 2010.

  1. Kablooie

    Kablooie Member

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    I have a 2004 Prius with the original read 12V battery. It's now about 6 1/2 years old.
    I checked the voltage and it reads 13.8/9 so it's fine for now.

    When the battery wears out is the car completely incapacitated or is there a period where it will run but doesn't work as efficiently?

    I'm asking because I'm wondering whether I should replace the battery now while it's still good or wait until it wears out?
     
    #1 Kablooie, Aug 31, 2010
  2. SW03ES

    SW03ES Senior Member

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    I would just replace it now. Why chance being stranded somewhere?
     
    #2 SW03ES, Aug 31, 2010
  3. fuzzy1

    fuzzy1 Senior Member

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    13.8V sounds too high. Are you sure the ignition is turned off? Have you let it sit overnight before measuring?
     
    #3 fuzzy1, Aug 31, 2010
  4. andyprius

    andyprius Senior Member

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    That;s a great battery! however it is way overdue for a replacement. Read the voltage when the car is in the standby mode. That is NOT READY. Using a meter should show something over 12V, in standby or acces mode. In ready the HV Bat takes over and attempts to charge the 12V bat to the reading you obtained 13.8 Volts or something around that figure. It does not mean your aux bat is OK and now reading 13.8 volts. It means only that the HV is charging at a rate of 13.8 volts. You can safely drive with a static, no load voltage reading of 12 volts BUT other wierd problems can unfold. Change it now! :cheer2:
     
    #4 andyprius, Aug 31, 2010
  5. eak354

    eak354 Member

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    I just replaced the 12V battery of my '04. I was listening to the radio on standby mode, and it just died. when i tried turning it on to ready mode it wouldn't. after around 10 minutes, it was able to go into ready mode.
    i checked the battery (on standby) with lights on, it went down to below 10v! that's when i decided to drive to the dealer and get a new battery. they charged me $200 for the battery, and said labor would cost and extra $100! i replaced it myself.
     
    #5 eak354, Aug 31, 2010
  6. richard schumacher

    richard schumacher shortbus driver

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    #6 richard schumacher, Aug 31, 2010
  7. dogfriend

    dogfriend Human - Animal Hybrid

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    I believe that experiences from others on the forum have shown that there will be a subtle degradation in mileage as the HV battery has to expend more energy to try to recharge the failing 12v battery. As the battery degrades further you may get strange warning messages and/or the red triangle of doom because the 12v battery is no longer able to supply enough voltage. At the very end, you won't be able to get Ready mode.
     
    #7 dogfriend, Aug 31, 2010
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