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MPG dropped after fixing hybrid prius 2007 battery

Discussion in 'Gen 2 Prius Main Forum' started by LillyWhite, Nov 26, 2018.

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  1. LillyWhite

    LillyWhite New Member

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    I have read many forums on here and find the knowledge very helpful. So helpful that we decided to fix our hybrid battery ourselves last week. We used Dr. Prius app to see which module was low. We used videos to get the car apart and rebuild the battery. We got one from Ebay with 7.9V and replaced that with our low one. All of our modules were above 8V except number 14, which was at 6.88V. We switched that one out for the one we bought on Ebay, after charging it up a little bit to match the other voltages.
    Everything seemed to go fine, and still through using the Dr. Prius app the module voltages are all within about .2 of each other. The weird thing is that our MPG has dropped almost by 10. We were getting about 42-45 before on the highway, and after a 10 hour trip with the same driving style we got about 35-37 MPG. That seems a little weird to me and I am wondering if something is still wrong with the hybrid battery. Does anyone know what could cause this? Also the screen shows that the battery is green a lot, and it hasn't dropped to pink/purple. It seems like when it is green on the screen, and when we accelerate, you would think it would drop to use the battery, but it would stay green while we accelerated. So it is almost as if the battery isn't really being used. Seems odd to me, and the outside temperature was 45 degrees.
    Any ideas?
    Thanks for the help!
     
    #1 LillyWhite, Nov 26, 2018
  2. Skibob

    Skibob Senior Member

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    I’m pretty sure when you repair the battery the battery computer needs to relearn the battery. Also the Prius will get lower mileage in colder weather. Look around the site, plenary of threads about it.
     
    #2 Skibob, Nov 26, 2018
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  3. bisco

    bisco cookie crumbler

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    does the dr prius app allow you to load test the battery? all green means the battery isn't being used enough.
     
    #3 bisco, Nov 26, 2018
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  4. PriusCamper

    PriusCamper Senior Member

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    Hmm... Haven't heard of this one... Usually you get a warning light and error codes... If you haven't already, disconnect the 12v for 5 minutes, which will reset everything. Sometimes after battery work it takes 70 miles or so for everything to get back on track... Or maybe more air in the tires?

    Anyways, congratulation on learning how to fix your own battery pack. Not any easy thing to learn... If the problem doesn't resolve itself, next step would be battery re-conditioning. You can either do that for each individual module with a smart charger for NiMH batteries that are commonly sold for RC cars, or you can recondition the whole pack at once without removing it from your car with a more expensive charging / discharging system you can learn about here: FAQ
     
    #4 PriusCamper, Nov 26, 2018
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  5. LillyWhite

    LillyWhite New Member

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    How long does it take to relearn the battery? We drove about 10 hours on it
     
    #5 LillyWhite, Nov 26, 2018
  6. LillyWhite

    LillyWhite New Member

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    Okay good to know, I am not aware of that, so I am assuming it doesn't let you test that. Basically we watch the battery for the modules as we drive it, so is it being tested under a load while we drive? I'm unfamiliar with this
     
    #6 LillyWhite, Nov 26, 2018
  7. Raytheeagle

    Raytheeagle Senior Member

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    Welcome to Prius Chat (y).

    Some questions:
    • Did you balance the pack or simply swap out the bad and input the new?
    • What are your long term plans for your Prius?
    • What reliability are you looking for in this module replacement?
    • What do you know about the module you input into the pack, like internal resistance, or how old it is?
    My bet is this will be the first of many trips into the battery pack:(.

    Good luck and keep us posted (y).
     
    #7 Raytheeagle, Nov 26, 2018
    05PreeUs, padroo, SFO and 1 other person like this.
  8. 05PreeUs

    05PreeUs Senior Member

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    The computer re-learns with each TRIP (key cycle w/ cold soak to fully warm engine). The car may be trying to re-balance the HV pack, if you did not do so yourself. You also may just have a low tire ;)
     
    #8 05PreeUs, Dec 1, 2018
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