2015 Prius on replacement battery not getting good mpg

Discussion in 'Gen 3 Prius Fuel Economy' started by Roger Elliott, Feb 2, 2026 at 11:05 PM.

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  1. Roger Elliott

    Roger Elliott Junior Member

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    Hi Folks
    I have a 2015 Toyota Prius with a replacement battery (actually 2nd replacement - first replacement was defective and replaced for free). I am running stock dimension tires but they are by a company called Sailun (Trezzo h408 size 195/65). Since the 2nd replacement, in my usual commute of 10miles, stop and go with some hills, I've been lucky to get 40mpg. Usually I would get 42-45 but now I'm getting like 36-39. The car has about 150k on it. Weather is pretty mild usually except in summer when it hits 100 or more. Any ideas?

    Thanks
    Roger Elliott
     
    #1 Roger Elliott, Feb 2, 2026 at 11:05 PM
  2. ASRDogman

    ASRDogman Senior Member

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    2nd replacement? So you got a used battery? Never worth it.
    You need the Sodium Ion NEW battery pack.

    Never heard of that brand of tire. Tires are important to fuel mileage.
    What tire pressures are you running?

    Both will highly effect mpg. Cooler weather effect mpg also.

     
    #2 ASRDogman, Feb 3, 2026 at 7:32 AM
  3. indel

    indel Member

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    Are these battery replacements OEM? Were they replaced by the dealership? Post some results from Dr. Prius app or Hybrid Assistant.
     
    #3 indel, Feb 3, 2026 at 9:32 AM
  4. Mendel Leisk

    Mendel Leisk MMX GEN III

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    Just to clarify: you replaced the hybrid battery, or 12 volt battery?
    Off-topic, but if you haven’t: I would clean the EGR (Exhaust Gas Recirculation) system as soon as possible, and replace engine water pump and thermostat.
     
    #4 Mendel Leisk, Feb 3, 2026 at 10:28 AM
  5. VelvetFoot

    VelvetFoot Active Member

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    So, what do the tires have to do with it?
    You did something, battery, tires, both at the same time? Correlation to cause and effect?
    This is actual mpg, miles/gals, full tank?
     
    #5 VelvetFoot, Feb 3, 2026 at 11:04 AM
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