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Advanced 12V battery testing?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by spycake, Jul 12, 2016.

  1. spycake

    spycake Junior Member

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    I just bought a used Prius, and took it to my mechanic for an oil change and standard inspection. They told me "the 12V starting battery fails a load test under 7V@150A" and recommended replacement. But the seller had mentioned he had the battery replaced not long ago, and indeed the service records indicate it was replaced only 2.5 years ago. So I ran the maintenance mode check described in this thread:

    Entering Maintenance Mode (aka 12V Battery Check) without Switching Headlights ON/OFF | PriusChat

    And I got normal values, 12.6 initial value and 11.3 after I turn the headlights on, tested after the car had been off for awhile.

    Is there something else I should do to test the battery? I don't really have any special tools for further testing. Should I just buy a replacement and plan to change it before winter regardless?
     
    #1 spycake, Jul 12, 2016
  2. Mendel Leisk

    Mendel Leisk Senior Member

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    Solar BA5 is a prosumer level digital load tester worth considering, if you want to invest around $60. At least start with a digital multimeter; something around $20~30 will do, and has multiple uses around the house.

    Then there's smart chargers..., it's a slippery slope, lol.
     
    #2 Mendel Leisk, Jul 12, 2016
  3. bisco

    bisco cookie crumbler

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    The Prius doesn't put much load on the battery. I would buy a volt meter and test it cold, under the hood. If it's 12.4 or better and you aren't having problems, leave well enough alone.

    Did you take it to a Toyota dealer? is it a Toyota battery? Might be under warranty.
     
    #3 bisco, Jul 12, 2016
  4. JC91006

    JC91006 Senior Member

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    Charge the battery and let it play out. I had a similar scenario when testing my Prius battery at Autozone, it tested bad. This was 3 years ago and it's still going strong in my car, always above 12.6v.

    I think those load testers put too much of a load on the small battery. The prius battery doesn't do much, just starts the computers.
     
    #4 JC91006, Jul 12, 2016
  5. andrewclaus

    andrewclaus Active Member

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    Just my thought; the 150 Amp test is invalid for the Prius. The Prius battery never cranks an engine. It boots up computers and runs some accessories like fans and lights in ACC mode. It could be very important for braking too, I think.

    I would not put any credence in that test. And I would be a little peeved it was performed in the first place.

    Edit: I see "the dog" just beat me to it.
     
    #5 andrewclaus, Jul 12, 2016
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