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Easy way to test for a bad cell

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Chris Vedeler, Feb 11, 2024.

  1. Chris Vedeler

    Chris Vedeler Red Pepper

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    2008 Prius
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    I got the "triangle of death" in my 2008 Prius. When checking the ODBII I got the following codes:
    P0A80 - Hybrid battery pack deterioration
    P3015 - High voltage battery module 5 fault: Battery block 5 malfunction
    P3000 - High voltage battery fault: HV battery malfunction

    Everything points to a bad cell or cells.

    I removed the hybrid battery and tested the voltage across all the 28 cells. They all tested at 8.01 - 7.87 volts. All basically testing fine as far as voltage. Of course that doesn't mean much. It is what the cell does under load that matters.

    So I went to Youtube to see if there was a way to test the cells under load, or to test the internal resistance of the cells without expensive equipment. The best I could find was using a 12volt light bulb and then seeing how much the voltage dropped over a few minutes. This seemed like a lot of time and wouldn't tell the the resistance in the battery cells. I then remembered I had a 12volt battery tester from Harbor Freight that does test the internal resistance of 12volt batteries. I figured 8 volt cells couldn't hurt at 12 volt tester, so I checked all my cells using it and it worked great!

    Here is a Youtube video I made showing how it is done.

     
    #1 Chris Vedeler, Feb 11, 2024
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  2. dolj

    dolj Senior Member

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    Thanks for sharing that. It looks like a very convenient way of getting some consistent numbers on each module.

    Just for people coming along afterward and for the sake of consistent terminology, the OP means modules where he states cells.

    A Gen 2 Prius has a battery comprised of 168 1.2 V (nominal) cells. There are 6 of these cells packaged in a module. There are 28 modules. Modules are paired into blocks for monitoring by the battery ECU. There are 14 blocks in the battery. Battery modules are counted from the right side of the car being number 1 to the left. Number 14 is nearest the electronics bay on the left side of the car.
     
    #2 dolj, Feb 11, 2024
    Last edited: Feb 11, 2024
    rayluo, Brian1954 and Chris Vedeler like this.
  3. Chris Vedeler

    Chris Vedeler Red Pepper

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    Thank you for the correction dolj.
     
    #3 Chris Vedeler, Feb 12, 2024
  4. rayluo

    rayluo Junior Member

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    2007 Prius
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    Glad to see this community still going strong (as our beloved Prius)!

    Chris, your test method was indeed creative. But are there devices more suitable for this kind of testing? The battery tester you used was originally designed to test the 12v starter battery, not for a 7.2v (nominal) module. Other than worrying about the reading would be inaccurate, I do not know how that "500A cold cranking amp" was tested, and I wouldn't attempt (until I watched your video) to use it, for fearing that it would draw too much amps from the battery module thus potentially damaging it.

    In a broader sense, my question is on how to evaluate the module's health. I had a batch of spare modules. After reconditioning, they fall into these 3 groups:

    1. Some can provide 5+ Ah power when discharging to 6V. I believe these modules are still in good condition.
    2. Some can only provide 2.5 Ah power when discharging to 6V; but they can still approach 5Ah if discharging to 4.8V. Are they still good to be use?
    3. Some of them have a voltage lower than 1V (gasp!), and they do not take charge at all. Are these modules dead dead dead?

    A follow-up question would be, how do we deal with the modules in category 2 or 3? Any recycle facility can take them?
     
    #4 rayluo, Jun 8, 2024
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