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Some food for thought.... about mpg & cost of ownership

Discussion in 'Newbie Forum' started by ruggb, Mar 14, 2013.

  1. ruggb

    ruggb Junior Member

    Joined:
    Jan 4, 2007
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    Location:
    Cary, NC, USA
    Vehicle:
    2007 Prius
    Model:
    N/A
    My 2007 Prius has 128,580 mi. HV batt warranty was 7 yrs/100,000mi (not CA.) I average about 46mpg. The cost of replacing the batt was $3100. at dealership. Miles driven were ~70% hwy miles.

    OK, lets figure this out with a little help from an Excel spreadsheet.

    I won't bore u with the details, but @ $3.50/gal for gas, if I had another car that gave me 35mpg my total cost would be the same.

    The cheapest batt with self install is about $1200. An equivalent cost would get me a 41mpg car.

    IF U were to get 200,000 miles out of a batt, then the equivalent mpg would be 38.
    At CA gas prices of $4.50/gal and 150,000mi (out of warranty) the equivalent is 39mpg.

    None of this factors in any additional purchase cost.

    Do u feel lucky???
    Does this prove u can't beat the laws of physics??? energy in = energy out, and somehow ppl have figured out how to make it all equal.
     
    #1 ruggb, Mar 14, 2013
  2. ItsNotAboutTheMoney

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

    Joined:
    Jul 18, 2009
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    Location:
    Maine
    Vehicle:
    2010 Prius
    Model:
    II
    Yes, simplest way is to balance fuel + battery against fuel

    g/P + b/m = g/O
    => 1/P + b/mg = 1/O
    => O = 1/(1/P+b/mg)

    Where O = other car mpg, g $/gal, P is Prius mpg, b cost of the battery, m is miles battery life.

    I'm in a CARB 10/150k state currently and last time filled up with $3.709 gas.
    I drive more than 15k miles per year.
    Let's say 50mpg (I actually get 52mpg with a bit of hypermiling)
    Assume $3.5k OEM battery replacement.

    Then
    O = 1/(1/P+b/mg)
    = 1/(1/50+3500/(150000*3.709))
    = 38.03

    We weren't getting 38mpg average in our Civic, although I did get a couple of 44mpg tanks in spring commutes in the Civic. But then, I could beat 50mpg in the Prius too. ;)

    Plugging in 41mpg for a Camry Hybrid and you get 32.59mpg.

    As you identified, the key is low battery cost per mile, which is why the 10/150k warranty is so helpful and why I wouldn't recommend a Prius to a low-mileage driver.
     
    #2 ItsNotAboutTheMoney, Mar 14, 2013
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