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Possible bad AUX battery or parasitic drain!!

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Andrew863, Aug 9, 2021.

  1. Andrew863

    Andrew863 New Member

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    So a couple days my wife had a issue getting the key to read and go to ready mode so I changed the key battery. Then I did some research and some people said to look as the aux battery. So I checked it right after she drove the car and it was 12.7 volts. Then after setting for 24 hrs it was 10.5 volts. So I thought its a bad battery. The guy I bought the car from replaced the battery less then a year ago with a Toyota battery. This has me thinking maybe it is a drain then. I let the battery set for 10 hrs withe the battery un hooked from the car and it stayed up at 12.7. So could this still be the battery or do you think I have a drain and if so do you have any ideas?
     
    #1 Andrew863, Aug 9, 2021
  2. JC91006

    JC91006 Senior Member

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    you can get your answer by doing a load test on the battery. Most auto parts places can test it for free
     
    #2 JC91006, Aug 9, 2021
  3. sam spade 2

    sam spade 2 Senior Member

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    Well one would THINK that would be true.
    But the sad truth is that many places that test batteries don't do it right.
    It needs to be "hit" by the tester several times on a row and almost nobody does that.

    His "test" does tend to point to a parasitic drain.
    But a tiny one is normal.
    It still could be a failing battery.......but not likely.
     
    #3 sam spade 2, Aug 10, 2021
  4. bisco

    bisco cookie crumbler

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    it sure sounds like it. but without confirming with a load test, it could be that the battery just can't handle the normal drain.
    do the load test first, and hope it fails. finding a random electrical fault can be tedious to impossible.
     
    #4 bisco, Aug 10, 2021
  5. mr_guy_mann

    mr_guy_mann Senior Member

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    I would suggest having the 12V battery properly charged and tested. The two most common testing methods are 1) an electronic tester that uses capacitance to estimate a battery's "potential" capacity and 2) a "carbon pile" tester that applies a resistive load to the battery that is 1/2 of its CCA rating for 15 seconds. I would do both tests.

    Posted via the PriusChat mobile app.
     
    #5 mr_guy_mann, Aug 10, 2021
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