Immediate 12V replacement?

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by abdullah arslan, Dec 1, 2020.

  1. abdullah arslan

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    That's what I ll did first in the morning, yeah cold measurement is 12.79 and after surface charge 12.53

    I left the hood popped as Mendel said. I ll do double measurement: first, measuring w/out triggering any electrical process even keeping fob away (measured 12.79) , then I ll apply the instructions (measured 12.53)

    This time, we got the results after charging the battery Btw, I wasnt born as a car expert, this is a learning process and I learned a lot thanks to y'all
     
    #61 abdullah arslan, Dec 10, 2020
    Last edited: Dec 11, 2020
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  2. jzchen

    jzchen Senior Member

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    That's a good battery. Hooray!

    moto g(7) power ?
     
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  3. sam spade 2

    sam spade 2 Senior Member

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    Maybe not.
    IF.....he did something like turning the headlights on for a minute and it STAYED at or near 12.53 for the next several hours with the load back down near to zero......that does NOT indicate a good battery.
    Serviceable for a few weeks or months, probably, but a drop of .3 V that doesn't recover is NOT a sign of a totally healthy battery.
     
  4. abdullah arslan

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    We ll see it in oncoming months. And I just want to thanks again for all suggestions. After charging the battery, I can say a noticable improvement on mpg and hybrid system. For the recent trips (more than 70 miles) after that , the charging status of hybrid system was just one bar below out of full, which used to be two bars below in general
    Posted via the PriusChat mobile app.
     
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  5. abdullah arslan

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    Time to get a new 12V battery before winter. Had no starting problem since last winter but the lower mpg, and it now shows 14.8v in ready mode while driving. Also, by chance, I just found the last install date, which is June 2013. Thanks again
     
  6. rjparker

    rjparker Senior Member

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    At least you managed another year on the old battery. I would change it very soon. Eight year old agm batteries can fail you even with two hours of driving after parking for ten minutes at a grocery store parking lot. Then you are faced with buying something on the spur of the moment.
     
  7. sam spade 2

    sam spade 2 Senior Member

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    Winter has little bearing on the 12 V battery in a hybrid because it does not actually "start" the gas engine.

    And the voltage reading while running has NO bearing on the 12 V battery at all.
    That just tells you that the 12 V charging system is working. The battery itself could be totally shot.
     
  8. abdullah arslan

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    What changes the voltage then (other than the regular loads)? don't know detailed knowledge about it, guessing that if the 12v one is degraded, the inverter tries to charge it brutally. As a result, ICE spends more effort and so getting lower mpg
     
  9. rjparker

    rjparker Senior Member

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    You are right. If your 12v battery is failing, it will often draw excessive current. To get high current into the battery, the charging system raises the voltage. If the charging system is continuously supplying high current to the battery, mpg will suffer. A good battery in a low parasitic load environment will charge quickly and the charging system will lower its charge voltage.
     
  10. abdullah arslan

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    ordered an OEM one for 210 bucks, hope to get another 8 years if the car especially the traction battery can make it :D Right now, 253.5k mileage on everything original, installed OCC recently, cleaned intake, will clean EGR soon with new plugs and coils
     
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  11. sam spade 2

    sam spade 2 Senior Member

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    While that can happen, it is rare.
    More often, the failed battery will accept little to no charging CURRENT even though sufficient voltage is applied.
    No charge actually going into the battery and no strain on the charging circuits.
     
  12. sam spade 2

    sam spade 2 Senior Member

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    What exactly makes you think that ?
    It depends on how and WHY the battery has failed.......and your use of the word "often" makes your statement NOT true.
     
  13. rjparker

    rjparker Senior Member

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    Experience and I stayed in a Holiday Inn last night. 6A45E00A-6F0D-4732-956B-0AC074D9CA3F.jpeg
     
    #73 rjparker, Oct 14, 2021
    Last edited: Oct 14, 2021
  14. sam spade 2

    sam spade 2 Senior Member

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    My experience says:
    About the only reason a lead acid battery will draw excessive charging current is if the plates in one of more cells are shorted.
    The most common cause of THAT is sulfation.

    Since AGM batteries are WAY less prone to sulfation and should never "run dry" in normal use......
    I don't remember the last time I saw a battery fail like that.

    I have seen a really LOT of them refuse to take a charge though, meaning very low or no charging current flowing.
    Or what appears to be normal charging current that apparently isn't really DOING much of anything because little to nothing will come back OUT after the "charge".

    I prefer Marriott actually. :)
     
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