Immediate 12V replacement?

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

  1. edthefox5

    edthefox5 Senior Member

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    Yeah I don't get that 2 volt thing either the mfd is pretty close to what you really have.

    Your measuring from the front jump point to a good frame ground like the strut bolt above it? Its worth further investigation.
     
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  2. abdullah arslan

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    Hi again, I went to AutoZone to clarify the measurements. They said your battery and alternator are good, I saw the car-off measuring was about 12.3V and car-on was over 14.5V
    And I also checked from display, this time it showed 11.2V, I guess it's because of my 11-12 min drive to AutoZone.
    So what might cause this difference? Nothing like usb charger etc. plugged into the car.
    Note: we directly measured from the battery, not thru the fuse box

    Posted via the PriusChat mobile app.
     
  3. ASRDogman

    ASRDogman Senior Member

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    You can't go wrong getting the battery designed for your car, from Toyota.
    Average life for the original battery is about 6-7 years. From what I've seen
    here on Prius Chat.

    But if you don't want to do that, find one locally. If it goes bad, you won't have to
    ship it back to get your warranty.

    The cost difference in minimal, for peace of mind!

     
  4. cnc97

    cnc97 Senior Member

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    From personal experience, if you are seeing 14.5V while the car is in “Ready” mode at the battery, replace the battery. The DC-DC converter is attempting to charge a battery that will not accept a charge. That’s where I was at 10 days ago. 14.5-14.7. ICE running when temp and battery level said it should not have to. With the 12v replaced, seeing 13.98 v in ready and economy is up 4 mpg. And, as an Autozone employee, I’m surprised that they would even test your 12v while installed. Our regional office(Louisville, KY)says that we are not supposed to attempt to test or replace the 12v in ANY hybrid vehicle. Not to mention the yellow sticker on the test equipment saying not to as well.
     
  5. ASRDogman

    ASRDogman Senior Member

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    Autozone quit testing the abs system so you can tell which sensor is bad.
    But, they will sell you a tester so you can test yourself! :)

    I bought one a few years ago that works fine! It was about $40.
     
  6. cnc97

    cnc97 Senior Member

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    I’ll gladly walk out with a customer and help or test whatever they need. I prefer to find a reason for the customers to keep coming back, instead of going to the other guys. At my store they need only walk 250 feet. We share a common lot entrance with an O’Reilly Auto Parts.
     
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  7. ASRDogman

    ASRDogman Senior Member

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    The one store close to me is pretty good. I've been going there for decades.
    MOST of the people that work there know what to do, and if they don't, they get the manager.

    I got some kid that ordered from the wrong store, so I had to wait for today to get it.
    And I decided to get both hubs, instead of just one. I told him I wanted the MOOG one!
    Not the cheapo durolast one, with a 1 year warranty.
    So when I went this morning, 1 Moog, 1 duralast. But they guy did order a Moog one and had
    it by noon.
    I'm glad it was cooler!
     
  8. rjparker

    rjparker Senior Member

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    I would look for a date stamped on your 12v battery even if it means taking it out. Odds are good its been replaced at least once in a ten year old car. If its four or five years old and not a Toyota battery I would order a new Toyota battery. It does not have to be immediate since it has not failed you yet. Cold weather is hard on batteries even though this one does not experience heavy loads.

    It would have been better to test at the fuse box with autozone's meter. You could check with your meter at the same time to verify your meter's accuracy. There is something going on with the mfd display's 2v battery reading discrepancy. As noted in my test earlier, the ecu's voltage monitoring accuracy is very good. Reading, generating and converting voltage is in the dna of a Prius.

    You could use your meter and measure the battery followed by the fusebox. If the readings at the fuse box match closely with the readings at the battery then I would not worry about the mfd reading problem until and if you have an actual problem of some kind.

    However...
    Loads on the 12v battery should not cause the large voltage difference you are observing. A bad connection could, operator error could, a faulty meter could or a bad ecu could. The readings should be closer to a 0.020v difference, not 2.000v that you were seeing, which, if real, would represent a 17% loss somewhere in the wiring or ecu calibration.

    PS - Next time the kid at autozone informs you your alternator is good, tell him you don't have one so it can't be good or bad. He also should not bother checking your fan or serpentine belts. The starter will be difficult for him to look up as well.
     
    #28 rjparker, Dec 2, 2020
    Last edited: Dec 2, 2020
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  9. sam spade 2

    sam spade 2 Senior Member

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    12.3 might qualify for OK......but it is definitely NOT "good".......in there indeed was no load or a very light load.
     
  10. sam spade 2

    sam spade 2 Senior Member

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    BAD assumption. That might also just indicate that the battery is a little low and it's trying to "catch up".
    That single piece of information is NOT enough to call the battery "bad".
    Seeing a charging voltage above 14 is quite normal......if it doesn't persist very long.
     
  11. cnc97

    cnc97 Senior Member

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    Mine did it for 7 days before I condemned the battery.
     
  12. abdullah arslan

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    Thanks, I think I ll look around the battery for the time stamp. Looked over all the records of the car, and didn't see any battery replacement. Then asked the previous owner (after digging up emails) and she said "we did change but dont know remember the date". Btw, the battery is and OEM TrueStar
    I later realized the alternator thing, too. Next time I should specifically ask for alternator test :D
     
  13. edthefox5

    edthefox5 Senior Member

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    The definitive test for a 12 volt battery is to buy a good battery maintainer and get used to seeing how long it takes to light up the full light. See if it’s capable of reaching a full charge.
    If all of a sudden it can’t reach full it’s telling you it’s tired and the last thing you want in your life is for the12 volt battery to leave you stranded.
    The horror storys we see here on this site are ridiculous.

    it’s a good idea to throw a 12 volt maintainer on the car at Least once a month
    Especially in frigid areas. Pay attention to how it acts.
    Cars take a lot of maintenance. Put mine on the car last night as we have a sudden cold snap 40 degrees which is cold for us. It took most of the night but I have a green it’s full light this morning.

    I agree with the poster about the charging voltage that’s too high.
    I agree that 12.2 volts is too low. It’s not horrible but it’s tired and no longer capable of taking and keeping a good charge. It may respond to a recondition
    Though.

    A healthy 12 volt battery in a Prius lives at 12.6 volts.

    my latest battery tender is a CETEK MUS 4 has recondition mode
    Amazon.com. I like it has a few different modes and recondition mode.
    It works well. Had it about a year now.
     
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  14. abdullah arslan

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    I really like the idea of battery maintainers, so looking for those to charge it fully. Did some research and some of them claim fixing the battery also. I am sure there are some posts about it but do these maintainers really work on Prius? I.e. saw a solar model just hung on the windshield and charges thru cigarette socket. Eager to try this on my car since we live an apartment, because cable throughout the building would be strange :)
    Posted via the PriusChat mobile app.
     
  15. ASRDogman

    ASRDogman Senior Member

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    If you drive the car a lot, you won't to to maintain the battery.
    If it sits for days at a time, then the solar one will keep it charged up, at a low amperage.
    But it sounds like the battery you have now is getting weak.
     
  16. Grit

    Grit Senior Member

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    o_Oo_Oo_Oo_Oo_Oo_Oo_Oo_Oo_Oo_Oo_Oo_O
     
  17. jzchen

    jzchen Senior Member

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  18. rjparker

    rjparker Senior Member

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    I assume the only real problem you have is the mfd screen shows 2 vdc low but voltmeter testing shows good. Plus the auto supply testing was good. And you have no starting or other issues.

    The charging system on the Prius is quite sophisticated and probably does not need a battery maintainer unless the car is not driven for weeks at a time. A top quality agm battery like Toyota sells will often given you five to seven years of service. My v went seven years. Ensuring there is not an excessive continuous current draw is important, which usually comes from hatches not totally closed, map lights manually turned on or an obd2 module left plugged in that does not go into sleep mode.

    Solar might be ok if it drives a properly staged charger. Meaning it periodically changes its voltage to electronically exercise the battery. Many chargers can actually hurt the battery if left on too long. Ideally it is designed for agm batteries as they often have a slightly different float voltage.

    You would need to wire it directly to the fuse box constant power or to the battery. Some come with a ring terminal cable and a quick connect expressly made for this purpose. The "cigarette" power outlets in a Prius are disconnected when the car is off.
     
    #38 rjparker, Dec 5, 2020
    Last edited: Dec 5, 2020
  19. rjparker

    rjparker Senior Member

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    Here is a $18 devive for those truly obsessed. "Battery Tender Wireless Battery Monitor." Its a small module that monitors your 12v and uses push notifications to your phone. Apparently reliable after a rocky start in 2017.

    An extensive Amazon review in the attached pdf.

    A4453782-EA0E-4C3E-8C92-7D5BAC6B0082.jpeg

    55EC49A8-5781-4D32-9323-39FB4F3F504C.jpeg
     

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    #39 rjparker, Dec 5, 2020
    Last edited: Dec 5, 2020
  20. sam spade 2

    sam spade 2 Senior Member

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    Yes, they all will work on any automotive 12 V battery.

    BUT.......the "fix" functions are mostly "shake oil".

    And your cigarette lighter socket is not HOT when the car is OFF so you have to connect that solar model at some other point.
    Or maybe re-wire the socket.
     
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