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Generation II Battery - Repair it yourself!

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by David Guybumbling, Oct 11, 2014.

  1. David Guybumbling

    David Guybumbling New Member

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    2005 Prius
    Model:
    IV
    I am a proud 2005 Prius owner and at 192k miles the Hybrid Battery finally crapped out. :(

    I spent a couple weeks researching and pricing (I have a second car):
    Dealership - quoted me $2,800 after the core credit
    Hybrid Rebuild Companies - $1,200 to $1,800 to take out, rebuild and re-install
    Used Batteries - $600 to $1,000 (installed by local shops)

    All seemed pricey, so i researched what it takes to repair the battery pack myself:
    28 cells in a prius generation II battery
    Each cell is independent and strung in a series and easily replaced
    Per cell cost ranges from $37 to $45 plus delivery cost.

    I looked up various instructional videos and safety information available in the 'Googles' :)

    I decided to DIY repair. 2 hours of labor and 1 bad cell - total cost $53

    _______________________________________
    EDIT to remove offers of services for a price: No self selling yourself or services on Priuschat
    _______________________________________
     
    #1 David Guybumbling, Oct 11, 2014
    Last edited by a moderator: Oct 11, 2014
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  2. valde3

    valde3 Senior Member

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  3. David Guybumbling

    David Guybumbling New Member

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    Agreed, by all rights and specs it is a good idea to have all cells balanced and conditioned. However, in a rechargeable system and for the purposes of this repair, the only thing required is the voltage measurements to be the same. I and 3 others I know have performed this same fix now and the system charges all the cells up without issue.

    As for capacity, over time, cells will fail and in just a year of use, cells are out of sync on total capacity. This is why single cells are failing and not all cells lost at once. The only real issue is the voltage which leads to the resistance and the heat if one or more cells are out of whack and exhibiting low voltage.

    This was the case in my battery pack where all cells tested at 7.7v with the exception of the one bad cell testing at 6.4v and which likely had a short as my fan was blowing almost immediately once the car went under load (not to mention the Christmas tree of lights on my dash).

    Bottom line, no risk to life, limb or property with all cells testing at 7.7v. While capacity issues may lead to other cells failing sooner rather than later as they age, so no real loss there. And, the state of charge of each cell will balance during the charging process within the vehicle - Take on a long drive up a mountain and let her coast down in Engine Brake mode.

    I choose to replace cells as they become an issue as this is a used battery in a car with 192k miles and likely not something that needs another 10 years of battery life. I expect to get at least 2 years or 24k miles out of this $53 fix. And that is fine by me!
     
    #3 David Guybumbling, Oct 11, 2014
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  4. CrazyLee

    CrazyLee Member

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    Vehicle:
    2004 Prius
    Model:
    II
    Some caution is necessary though. The HV battery has a minimum 206 volts at the terminals. Yes there is a relay the separates the "hot"
    terminals to the "cold" terminals that go to the cars electrical system. But a simple slip of a screwdriver or other tool can unleash hundreds of AMPS of current in a big flash!

    Those 1000 volt gloves would be most appreciated in this case because 200 volts will instantly kill you if the voltage goes through your body.

    If you do not have electronic or electric training you could put yourself in a bad situation. If there is schooling available it will be to your benefit since understanding how those invisible electrons behave gives you a better understanding of how the Prius does its job.

    Read everything you can here on PC as the info is outstanding. (Thanks to all the posters, I have learned a lot here too.)

    So, be SAFE and I hope this this works out for you.
     
    David Guybumbling likes this.
  5. dolj

    dolj Senior Member

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    I have to disagree, unless there is a rebalance phase in the charging cycle, this won't happen. Also Engine Brake mode will charge less not more and certainly will not contribute to rebalancing. The only way to rebalance as far as I know is to use an external charger and do a cycle of discharge -> charge -> partial discharge (to bring back to 80% capacity).

    As a point of clarification, you talk of cells, when you mean modules. The Prius Gen II battery is made up of 28 6-cell modules. :) Maybe you could edit your posts to reflect this to avoid confusion for readers.
     
  6. David Guybumbling

    David Guybumbling New Member

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    So, in a 1 year, 3 year, 5 year or 8 year old battery...are you saying all the cells are balanced perfectly? I have to disagree. The 'Modules' (to correct myself and adhere to proper technical semantics) each degrade over time at different rates and fail individually over time. This very fact negates the pro-shop's dire warning that somehow not balancing the capacity and the charge of each 'Module' will somehow lead to a catastrophic vehicle fire.

    I stand by the fact that the risk of run-away heat leading to fire is variances in voltage (a voltage drop) within the series of 'modules' leading to resistance. The charge and/or capacity is not a significant factor in the creation of resistance and ultimately the heating of the 'module' and those adjacent to a capacity deficient 'module'.

    This is a repair of a battery pack to extend the life of such. My opinion, based on my knowledge of electronics and research of these batteries, is that for this repair, it is far less economically efficient to spend $1,800 on a professionally reconditioned and balanced battery that they admit will likely fail in 24 to 36 months anyway; when you can simply replace the cells that are voltage deficient for $50 each as they die, especially when it is usually only 1 or 2 bad cells at the most.

    As for using the engine brake going down the mountain...have you let your Prius coast down a mountain?...Unless you are looking to replace your brake pads at the bottom, I suggest the engine brake...and it will charge your battery to the top of the green and peg it, and continue juicing it after it gets there. :) P.S. If you search for Prius Battery Modules to purchase, you will find that they are being sold as Battery 'Cells'. The industry of resale has decided to use these terms interchangeably...lol.
     
    #6 David Guybumbling, Oct 12, 2014
    Last edited: Oct 12, 2014
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  7. David Guybumbling

    David Guybumbling New Member

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    IV
    Very much AGREE with your warnings. IF anyone here does decide to do this yourself, be sure to use proper precautions (gloves being a reasonable precaution) - By all means, REMOVE THE ORANGE SERVICE PLUG BEFORE OPENING AND EXPOSING THE TERMINALS! And, test the internal and external terminals with a volt meter AFTER you remove the service plug to assure Zero Voltage.
     
  8. dolj

    dolj Senior Member

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    I am not disputing the use of 'B' mode as you describe it for descending a mountain, just the notion that doing this will somehow balance your batteries. The 'top of the green' as you put it will only be 80% charge and once at that point re-gen will cease and engine braking will be substituted to take the place of re-gen. This being the case, there is no opportunity for balancing.

    As for this:
    I am not saying any such thing and I have no idea to what you are referring. At the least, I don't think it was anything I said.