please advise with batteries maintenance strategy

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by mavalmir, Jul 24, 2022.

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  1. mavalmir

    mavalmir New Member

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    Hi everyone,
    I have Toyota Prius 2008 for 5 years. Now it has 211K miles.
    Lastly, I noticed the dropping in gas millage - now around 25-29 MPG.
    It could be different reasons for it:
    1. Recently I installed a new cat invertor from eBay (the original was stolen from my car). Probably bad cat invertor.
    2. Big battery is dying.

    I used Prius as my second car. Once or twice a week. And I checked Techstream metrics after staying for a week in a parking lot and after driving around 5 miles. I attached screenshots here.

    I found (thanks forum) 2 ways of maintenance of big battery life:
    1. Using grid charger (Maxx Volt, Prolond, DYI etc).
    2. Replacing some modules in the battery.

    Could you advise me which way is better for me (and my current metrics)? or both?
    I don't see that any modules have a huge drop from others.

    PS.
    Looks like 12v battery is dying as well (shows only 11.19V after staying one week) :(
     

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    #1 mavalmir, Jul 24, 2022
  2. bisco

    bisco cookie crumbler

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    if you're not getting any trouble lights, i would use a grid charger

    there are many other reasons why a prius loses gas mileage as well
     
    #2 bisco, Jul 24, 2022
  3. mavalmir

    mavalmir New Member

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    Could you point out any other reasons for the loss of gas mileage?
     
    #3 mavalmir, Jul 25, 2022
  4. nancytheprius

    nancytheprius Active Member

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    well start here. get the 12 V tested and replace if it’s needed.

    Also, does your car sit for long periods of time between driving? (like weeks?)
     
    #4 nancytheprius, Jul 25, 2022
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  5. bisco

    bisco cookie crumbler

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    tires, filters, plugs, injectors, throttle body and maf, brake drag. at 200,000 miles, everything is dirty or worn out.

    does she burn any oil?
     
    #5 bisco, Jul 25, 2022
  6. TMR-JWAP

    TMR-JWAP Senior Member

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    When the catalytic converter was stolen, what did you replace it with? Did you also replace the downstream O2 sensor? That sensor usually gets taken during the theft and the wires ripped out. I have seen some cats get replaced, without replacing the O2 sensor. This seems to cause a significant drop in MPG. Last car I saw with this went from 39mpg to 48mpg after a new denso sensor was installed.

    Do you do all very short drives? Less than 5 or 10 minutes?
     
    #6 TMR-JWAP, Jul 26, 2022
  7. mavalmir

    mavalmir New Member

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    thanks for all your answers. Please tell me a little more about the car.
    I use my car in the same style before and after cat was stolen.
    The thief was happen 4 months ago. I've replaced cat and O2 sensor (TMR-JWAP you're right they ripped out) from eBay. Some cheap aftermarket analogy ($150 + $20).

    Gas mileage with old cat was 36-40 MPG
    Gas mileage with new cat and new O2 sensor became 32-35 MPG
    Now is 25-29 MPG - that's super bad for Prius.

    I don't have any errors lights and thought that need some maintenance on the big battery
     
    #7 mavalmir, Jul 26, 2022
  8. bisco

    bisco cookie crumbler

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    can you detail for us the time period you noticed the mpg's going down?

    something like this:

    i was getting 36-40 with the old cat, then after replacing it, it immediately dropped to 32-35, then after X weeks/months, it dropped again to 25-29.
    or
    over X time period, it slowly dropped to 25-29.
     
    #8 bisco, Jul 27, 2022
  9. mavalmir

    mavalmir New Member

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    Thank you for your clarification.
    I was getting 36-40 with the old cat, then after replacing it, it immediately dropped to 32-35, then after 2 months, it dropped again to 25-29.
    Last 2-3 months I found that 12v battery is dying. I've charged it a few times.

    PS
    1. Prius burns a little oil, before replacing cat and now. something around 2 qt per 3000 miles
    2. I was and am using for short driving 5-15 min per trip
    3. My ABS pump works pretty often. I've replaced it with a used one from eBay almost 2 years ago (I have error lights)
     
    #9 mavalmir, Jul 27, 2022
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