Bad Hybrid Battery & Mileage Chart

Discussion in 'Gen 2 Prius Technical Discussion' started by Wayne, May 27, 2018.

  1. Wayne

    Wayne Active Member

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    My hybrid battery just died on my 2005 Prius (a generation 2 NiMH battery). With that ending I thought you might like to see my hybrid battery performance over the years, in the form of a graph of my mileage log.

    I live in Indiana, so the summers are warm and the winters are cold. Hence the jittery shape of my mileage chart. What I think I see on the graph is some natural loss of performance (trend line 1), some more abrupt loss of performance (trend line 2), and a perceived bottoming out of performance (trend line 3).

    Admittedly, as my mileage declined I may have become a more aggressive driver, as I could no longer set new records on this video game I was driving. That might account for trend line 2 degrading faster than normal. However, the end result of losing about 10 MPG was probably a warning that within the next few years my battery might die.

    Even with the decline in MPG, and the very low number of miles driven, I still saved almost $7,000 in gas over the small SUV I originally intended to buy when I found this car. And that's over only 82,000 miles (I think 13 years is what got the battery). So, no matter how the battery gets changed, I think owning the car was still very cost-effective!

    I'm capable of replacing the battery myself, but I'm probably going to be lazy and go the dealer route. I replaced the roof antenna, and that was nasty enough, lol. I hear the dealer installs new batteries, which get a 3-year warranty. That should give me plenty of time to decide if I want to replace the car or not.

    I am curious if I will get back into the 50's for a tank of gas after the battery is replaced. Anyone have any experience with that?


    Wayne's 2005 Prius Mileage.png
     
    #1 Wayne, May 27, 2018
    Last edited: May 28, 2018
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  2. fotomoto

    fotomoto Senior Member

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    Easily. BTDT with my 06. See the link in my signature for how that played out.
     
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  3. Aaron Vitolins

    Aaron Vitolins Senior Member

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    Thanks for the data! Did you always keep low rolling resistance tires on your prius?
     
  4. Wayne

    Wayne Active Member

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    I do not, and that may help explain some of the accelerated decline after 6 years, as the OEM tires were replaced inside of that circle, and there would have been a small bump down because of that. Obviously the curve continued to decline notwithstanding of the tires, but that may help explain some of the accelerated slope.
     
  5. bisco

    bisco cookie crumbler

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    nice graph, amazing historical data, thank you!(y)
     
  6. Aaron Vitolins

    Aaron Vitolins Senior Member

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    Okay good to know! I have had 3 prii in the past and with all of them I actually noticed a pretty big difference, actually a shocking difference in fuel economy with the wrong tires. I had a 2012 liftback that I bought with cheap Chinese tires and the poor car struggled to get 42 mpg cruising on the highway at 70 mph. I couldn't stand it so I bought some energy saver AS tires, and boy I was shocked. .I could get 50 on the highway pretty easily. Hell I drove from nashville to Cincinnati Ohio and managed 57 mpg. It sounds like a bunch of BS but I was really shocked my self!
     
  7. Wayne

    Wayne Active Member

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    Interesting result. A 15 MPG difference is pretty huge, all right! However, I wonder if some other factors may have been mixed into your success.

    In 2016 Consumer Reports found the difference between the lowest and highest rolling resistance tires they tested was around 5.7% MPG. For a 50 MPG car that would add up to 2.85 MPG. And that's the difference between the best & the worst. I started out around 55 MPG with new OEMs. Minus 5.7% I should have started out near 52 MPG in warm weather with a new set of the worst rolling resistance.

    So I'm thinking 15 MPG is pretty huge.

    Tire Rolling Resistance and Fuel Economy - Consumer Reports
     
    #7 Wayne, May 29, 2018
    Last edited: May 29, 2018
  8. Aaron Vitolins

    Aaron Vitolins Senior Member

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    The difference wasn't that huge in everyday mixed driving. That was just a trip for example. It was just possible to get far better mpg. Not that it go that much different mpg most of the time. It was more of a 6-8 mpg (for me) difference in mixed city highway tanks of gas.
     
  9. Wayne

    Wayne Active Member

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    I thought I'd update everyone on the results of my battery swap. As my mileage chart at the top shows, I hadn't seen a 50-MPG tank since 2011. Well, I have good news! My battery replacement made my 2005 like new again! (see below) :)

    Hope this puts to rest that the problem was anything other than my battery.

    One thing I really noticed is my ability to withstand a long fast-food drive-thru has improved markedly, lol. Even with A/C off, I'd see 1 bar remaining on the battery long before I escaped the line. Now with A/C off it's rock-solid, and with A/C on I lose maybe 2 bars. Maybe how fast your battery dies in a long fast-food line is one of the final clues as to whether your battery is about to give out on you.

    This particular mix of miles was about 40% highway (201 miles) and 60% city (306 miles). I waited a little over a week for the car to acclimate to the new battery before starting this tank. My goal was to get at least 500 miles under my belt before a refill. Math says I could have gotten 700 if I wanted to run it dry!

    Very happy. :)

    IMG_1677.JPG
     
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