More miles per tank after aux battery change..???

Discussion in 'Gen 3 Prius Technical Discussion' started by ilovevanhalen, Jul 30, 2025 at 1:08 PM.

  1. ilovevanhalen

    ilovevanhalen Junior Member

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    So I have a 2015 Prius, bought brand new in 2015. And just a month ago, my auxiliary battery (in the trunk) died and I replaced it with a geniune battery from the Toyota dealer. I noticed that after I fill up the tank to full and check the dash for miles left (countdown to zero), it's reading 500 miles. Which I know for a fact it was never that high. Does anybody know if there's something I need to reset or sync after an auxiliary battery replacement?
     
    #1 ilovevanhalen, Jul 30, 2025 at 1:08 PM
  2. Tombukt2

    Tombukt2 Senior Member

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    It happens all by itself with driving just drive the car you will settle in directly . Yes it all resets. If ya get better mileage now wen it drops again chk 12V again . Happens in my generation 2 after 12V disconnect
     
    #2 Tombukt2, Jul 31, 2025 at 7:20 AM
  3. ASRDogman

    ASRDogman Senior Member

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    Everything resets to factory defaults. After a few tanks, you'll notice it normalizes...
    Did you charge the 12v battery? Might be a good idea to charge it for 5 or 6 hours at
    5 amps or less. Then you KNOW it has a full charge.
    And since the inverter is not trying to charge a weak 12v battery, your MPG might
    actually increased the MPG...

     
    #3 ASRDogman, Jul 31, 2025 at 8:58 AM
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Have I got this right, you're upset by this?

    Anyway, yeah, miles-to-empty likely got reset to defaults, and will adjust over time. That said, a new battery "could" mean the engine having to work a little less, to keep it charged?

    Just 2 cents: I'd forgetabout miles-to-empty display, just keep an eye on the venerable gas gauge, and calculate the mpg for a few tanks.
     
    #4 Mendel Leisk, Jul 31, 2025 at 11:38 AM
  5. Grit

    Grit Senior Member

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    When you disconnect the battery, it lost history of drive style so it won’t be able to project or guestimate to DTE so it reverts to factory guesstimation. You’ll be sad once the 500 DTE is lowered. Mine is 550 mi to 600 DTE right after full up
     
    #5 Grit, Aug 1, 2025 at 12:38 AM
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