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    lmarcucci Junior Member

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    Hello everyone, I am planning to buy a prius that has a bad hv battery. I was wondering it was ok to drive it over 100 miles with a bad hv battery? What damage will occur if any? thanks!
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    seilerts Battery Curmudgeon

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    I just had a guy drive up from Abq on a bad HV battery, 55 miles and 2000 feet of elevation gain. I had to push it into the shop because reverse is basically doesn't work. It will be slow going but doable.
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    lmarcucci Junior Member

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    So, the computer does not adjust accordingly and just use the gas engine? or do you mean it will be slow going because the gas engine only produces 80hp?
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    seilerts Battery Curmudgeon

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    The computer does not use much the HV battery. That means that the engine is driving MG1 to send current to MG2, and then it gets complicated. How much actual power do you have? I don't know, certainly not 80 HP though.
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    Danny Hamilton Active Member

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    HV battery has to have enough power to start the gas engine (ICE) or you won't be able to drive it at all.
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    seilerts Battery Curmudgeon

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    Unless the car has been sitting for more than a year, it is fine for the HV battery. The 12V would be toast. Anyway, the HV battery will start the ICE, because there is plenty of potential in a car with a recently flagged P0A80, but it will not provide sustained current, because a bad cell acts as a resistor and heats rapidly under continuous discharge. The HV ECU drops into a fail-safe mode, similar to a limp-in mode for automatic transmission failure.
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    lmarcucci Junior Member

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    Great thanks guys. What do you guys think about buying a 200k mile 2005 prius with a bad hv battery? I want to fix it and then resell it. I am a computer engineer and know my way around electronics, So i will have no problem doing the repair myself with one of the many good writeups on it here, and around the web. I was thinking about just buying a used one with low miles and then rebuilding this one. But, anyway, is there anything i should look for when scoping out a prius to buy, and more importantly one with this many miles? I assume the engine is good for 300k at least since it is not on all the time and prius drivers don't have much of a lead foot. But, will i be able to sell it at the kbb of around 6k very easily or will it be hard? Thoughts?

    Thanks again.
    1 people like this.
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    cwerdna Senior Member

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    Do you have experience working with high voltages?

    What do you mean by "rebuild"? Are you planning to change out the HV battery pack or do something more? Do you have the necessary equipment to at least read the DTCs?
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    lmarcucci Junior Member

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    Nothing a good set of lineman gloves can't solve. Is there really anything else that i should protect myself with?


    I mean test each battery module and see which ones are substantially below 7.2v, then swap them out for new ones, then sell the battery.


    and yeah, i have a obd2 tester. That should be suffice, right?
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    cwerdna Senior Member

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    Failed traction (HV) battery, what to do? - Prius Wiki under rebuild it yourself has some potentially useful links. (If you find more, you're welcome to create an account on the Wikia and add them to the page.) I've never done it and wouldn't bother.

    If it were me and I wanted to bother w/fixing it myself, I'd likely go w/a rebuilt pack.
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    Flying White Dutchman Senior Member

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    ts : how you now its a bad battery?
  12. Offline

    seilerts Battery Curmudgeon

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    This method will fail if the battery has overheated several times in its life. A module with very low capacity due to electrolyte loss will still hold 7.2V+ for a long time, even if having less than half of it's original capacity. Best way to tell is to discharge-charge-discharge-charge, and measure the amount of Ah in the second discharge.

    If you have 1 module with less than 7.2V, then it might work. If you have more than 1 with less than 7.2V, that's an indication that the entire pack may be bad.
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    richard schumacher shortbus driver

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    I have to wonder how many people would buy a Prius with a battery that had been rebuilt by someone who had never done it before. Would they pay enough to make it worth your costs?
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    lmarcucci Junior Member

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    Not trying to be an asshole to the person who i sell it to or you, but why would i tell them? If it works it works. I was planning on buying a used pack and putting it in the car and then selling it. Then i would take my time with rebuilding the battery for learning purposes. If i felt good about my work i would then sell the rebuilt battery pack on ebay. You can't really screw someone over on ebay. If they don't like what they get they can always send it back and let paypal deal with you.

    Thanks a lot for the link. I'll read up. I was planning on reading up on the rebuild process before doing it. I wasn't going to fix the battery on whim.

    So, what is a sellable capacity for each module? Is the brand new capacity for each module in the 2nd gen 6.5ah? Do you think anything below 5ah would need replacing?
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    wegortw New Member

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    I wanted to see if I could get more details about possible problems of driving in limp mode? We bought a high mileage 2005 185k mile prius last week with no known issues. We since drove it 600+ miles over multiple trips int he past week and now the Christmas Tree lit-up - P0A80 (no second code of what pack for unknown reason). Problem is we are 300 miles from home and need to drive the car.

    - What damage will occur if continued to drive in limp mode?
    - Can we reduce the damage by continuing to reset or delete the code?

    As the car behaves fine after first reset, I believe this is because it takes two trips to compare errors based on the P0A80 error message "Voltage difference between battery blocks is higher than standard (2 trip detection logic)".

    Last question, we are getting different results from different OBD2 readers in our local auto part shops and I haven't yet figured out how to get the DTC Log to show me the specific battery details; but can I use the on-board Maintenance Mode to show me the battery details?
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    nh7o Off grid since 1980

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    I doubt you will damage anything. On the highway, going on fairly level grade, the best efficiency is had at the speed where there are no arrows going to or from the battery. At that point there is not much concern about the battery's health. It's accelerating up to that speed which will be slower, due to the limitation of the current from the battery. You may not make folks happy by going too slowly.

    As for codes readers, you must have a Prius specific reader to get to all the ECU's. A generic reader won't do it. The car will not display its own codes, which is somewhat lame, but that's how it is.
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    Jesse Melara New Member

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    I have a question...I am new to the prius family. I bought my 2007 prius a few months bad and love it. (although the seat is pissing me off lol) but I was wondering what are the signs of the HV battery going bad? I was wondering because when I am driving it, the battery gets fully charged, but when I leave it parked for a day or so, that battery seems to be on the last 2 bars...I am worried that it is a bad pack...what kind of test can I do besides taking it to a dealer?
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    SteveLee Active Member

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    Fast and large changes in the state of charge level seen on the MFD while driving is a commonly reported symptom of a weak HV battery. Typical SOC while highway driving remains mostly in the middle to upper area of the scale. City driving is often lower. Below 41 mph in cruise you would expect to see the engine cycle off for around 1 mile then cycle back on to recharge the HV battery. How about the MPG? Have you noticed any difference since you bought it? When you say "fully charged", on flat lands I seldom see the SOC indicating all the bars charged. Next to the top yes. Very occasionally the top bar, usually when coming off an off ramp while coasting a good ways.
  19. Offline

    seilerts Battery Curmudgeon

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    In an area with mountains, a dying HV battery will have its fan running on high a lot and have seemingly no power at a certain point when climbing a grade. Someone that knows what they are doing can estimate the amp-hour capacity remaining with the right scan tool. From the user standpoint, if you can avoid having situations where the battery fan comes on high, then you are doing your part to maximize the possible longevity. Otherwise, just drive it until it dies. If you don't want to fix it, then someone else will buy it for a pretty decent price. If you do want to fix it, find someone that does rebuilds with Gen III packs.
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    nh7o Off grid since 1980

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    Jesse, also I would recommend cleaning the battery cooling fan, which procedure has photos and videos here and on youtube. It will help to extend the life of the battery a bit. Heat is the enemy of the battery, so keeping it cool is important. Run the A/C in hot weather.

    Where is your location? Hot climate?

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