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2005 12V battery loses charge

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by atlsud, Jan 3, 2023.

  1. atlsud

    atlsud Junior Member

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    Hello,

    I was getting the lights on dash and display that indicate a dead 12v battery. Multimeter showed 4.8volts. Removed the battery and had Autozone charge and test. After a 3 hr charge, the battery tested good (can't believe they didn't try to sell me a new one). After driving less than 10 miles, I got the same warning lights and the voltage showed 10.6v, the car wouldn't start.

    Connections at the positive and negative battery terminals all look good and secure. Anything else I can check to troubleshoot?

    Is it possible that a good test at Autozone was incorrect? I would hate to start throwing parts at it.

    Thanks!
     
    Tombukt2 likes this.
  2. Tombukt2

    Tombukt2 Senior Member

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    Yes guaranteed that AutoZone was incorrect You need a 12 volt.
     
  3. dolj

    dolj Senior Member

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    A healthy 45 aH battery (or even the 36 aH battery in the non-SKS) cannot be charged up in 3 hours. Any knowledgeable person would know this.

    Who even knows how it tested 'good'? This battery is done for.

    Replace it then you can turn your attention to other things of more importance.
     
  4. SFO

    SFO Senior Member

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    How many miles on the vehicle?
    Generally, when you have warning lights you will also have related OBD2 codes stored. Do you have any codes that you can post?
    Again, warning lights usually mean there are codes stored. Find a hybrid compatible OBD2 scanner and post the codes in this thread.
    For a no start, have you checked both the AM2 and 'Dome' fuses?
    Check the negative ground strap (from the 12v battery), you may find a rusty/loose connection where it attaches at the body.
    How old is the existing 12V battery, and how many hours per week do you drive?

    My WAG is you may have a failing inverter coolant pump, which can store OBD2 code P0A93 in the ECUs (computers). But that is just a guess. If you can get the vehicle to 'ready', check to see if the pump is working by touching it with a finger/rod/pencil/stick to confirm there is a vibration, then check the inverter coolant pump reservoir for movement on the liquid surface. Just like 12v batteries, most pumps won't last forever, when was the last time the inverter coolant pump was replaced (approximate # of miles)?
     
  5. atlsud

    atlsud Junior Member

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    Thanks for the response! I have a new battery on order (DieHard EV Hybrid/Electric Battery: B24R Group Size, 410 CCA, 510 CA. $265)

    The voltage yesterday was 10.6 v, checked again this morning and the voltage was the same (measured via combo meter diagnostic)

    Does anyone know the minimum voltage for the car to turn over?
     
    #5 atlsud, Jan 4, 2023
    Last edited: Jan 4, 2023
  6. sam spade 2

    sam spade 2 Senior Member

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    More than possible. Likely.
    How old is the battery ?
    A new one would be a REALLY good gamble.
     
  7. sam spade 2

    sam spade 2 Senior Member

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    WOW. Talk about not seeing the forest for the trees......!!!!!

    A lot of really BAD advice in there because.............
    IF you aren't positively sure that your 12 V battery is healthy, you can't trust any codes that you see.

    First things first.
     
  8. sam spade 2

    sam spade 2 Senior Member

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    The engine does not start from the 12 V battery.
    It just "boots up" all of the computer boards.

    10.6 is WAY too low.
    12.0 is half discharged or less.
    A few people have reported trouble with a no-load battery voltage of 12.2 or 12.3 but that often will allow it to start.......maybe with some codes.

    P.S. It is normal for an old battery to "lose charge" just sitting.
    Or not to really charge up in the first place.
     
  9. atlsud

    atlsud Junior Member

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    Thanks all. Going to close this thread as the battery is not the issue.

    After a charge, the battery was holding voltage. When the ICE was on the voltage on the 12V was reading a steady 14.1-14.4V (via combo meter). I drove for a few minutes and the red triangle and yellow circle were lit 12V battery was still show good voltage
     
  10. sam spade 2

    sam spade 2 Senior Member

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    Good luck with that.

    Your previous readings did NOT indicate that it was holding a charge.....at least not for long.

    And while the car is "running" or in ready mode, the voltage at the battery is the CHARGING voltage NOT the battery voltage.
     
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  11. dolj

    dolj Senior Member

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    This is blatantly false information and is total BS. A gen 2 will quite happily start right down to 10.5 V. 12.2 and 12.3 will NOT cause starting problems period.

    However, just from the battery perspective. it is not good for the battery to be discharged to this level. It needs charging.
    What was the voltage at this point?
    What was the voltage at this point?
     
    #11 dolj, Jan 5, 2023
    Last edited: Jan 5, 2023
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  12. sam spade 2

    sam spade 2 Senior Member

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    How many Gen 2 vehicles exist ?
    Have you surveyed ALL of them to arrive at this conclusion ??
    I think not......and your "absolute" conclusion is just a guess.
    And not a very good one at that.
     
  13. dolj

    dolj Senior Member

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    You don't need to survey all Gen2's and the experience here collectively is far greater than your minimal (if any) experience with the inner workings of the Gen 2 model.

    You've been asked many times to cease and desist trolling the Gen 2 forum with inaccurate claims.
     
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  14. sam spade 2

    sam spade 2 Senior Member

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    Sorry but that's not the way a public forum works.
    You can not silence opposing opinions by telling them to "shut up and go away".
    There is no trolling involved.

    And it is YOU that is doing the biggest dis-service to the community here by stating as absolutes things that are NOT.
    Like "a gen 2 will never have a problem if the battery is between 10.5 and 12.0 volts" because THAT is blatantly not true.
     
  15. SFO

    SFO Senior Member

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    If you have a local dealer, they may offer a less expensive OEM battery option. Call and check.
    Which App are you using, as you may be using an App that isn't fully hybrid compatible. Also, which warning lights are being displayed?
    If the vehicle is starting again, then just skip the fuse checking. Yes, a bad fusable link would prevent the vehicle from starting. Both fuses (Dome and AM2) will be found inside the vehicle, or under the hood. Given your early model year, there will be another fuse to check, AM1.

    Do you have a multimeter, which would allow you to check for quiescent drain current?
    6 yrs is quite a stretch for a YT battery, best to just change it and see if the issue(s) go away. Generally speaking, 10+ hours per week should be enough to keep a 12v healthy, and means you likely need a new 12v battery. Does your 12v become 'hot/warm' at all?
    This would be the upper end for known pump failures, but you can also give the VIN to the dealer and confirm that they've changed it once before during a 'service campaign'. Most OEM pumps will last around 100k, some less and others more. Aftermarket is hit or miss all told.
     
  16. Mendel Leisk

    Mendel Leisk Senior Member

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    Checking voltage first thing in the morning, with the car off, is more telling.
     
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