Is my 12v battery dying? A/C settings getting lost and 14.7 volts..

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by BrickedKeyboard, Apr 15, 2019 at 11:53 PM.

  1. BrickedKeyboard

    BrickedKeyboard New Member

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    I noticed this morning that the climate control was set to "off". I normally leave it on "auto". And this afternoon, when I got in the car again, same story - back to "off". I didn't touch it.

    The battery is 7 years old and I also have noticed that my inverter, which I have plugged into one of the accessory plugs that is off when the car is off, shows 14.7 volts now after a 40 minute trip.

    I suspect this high voltage is the car trying to charge this failing battery which now has high internal resistance and thus little current is flowing.

    Another question: Pep boys lists this battery, "ACDelco Red BCI Group 51 Battery" as "compatible" with my vehicle. I can't find any information on this battery. It's suspiciously cheap ($91). Is this even an AGM? Does it even have the correct vent tube? Do the posts even fit?

    But I'm tempted, even if the life were 2 years less, it's 60% cheaper than the Bosch. But the Bosch is listed as being the real deal and is supposed to be AGM, with the vent tube, and the longer warranty, etc, etc.
     
  2. bisco

    bisco cookie crumbler

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    best way to test the 12v is at the jump point under the hood in the morning before starting the car. if it's 12.5 or better, you're fine. but replacing a 7 year old battery prophylactically isn't a bad idea.

    no idea what's going on with you're a/c setting, that is an odd one.
     
  3. Rebound

    Rebound Senior Member

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    But if you cover a battery in rubber, it won’t work!

    Seriously, I know that the battery voltage is over 12V. It’s a good idea to replace at the first sign of gremlins, or else the car won’t start and you’ll be stranded somewhere.

    If you don’t buy Toyota’s, Optima Yellow Top is the replacement battery most people go with.
     
  4. sam spade 2

    sam spade 2 Senior Member

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    12.0 Volts is roughly half discharged.
    "over" 12 volts isn't good enough.

    And I don't agree with your conclusion about " most people".
    Optima doesn't have a really good reputation for reliability.

    Seems like a lot of owners have good luck at Pep Boys.
     
  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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  6. BrickedKeyboard

    BrickedKeyboard New Member

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    Thanks. Seems like a pretty clear thing to buy. In my experience the determine factor for if a 12v lead acid battery works is how fresh it is and not the brand. Not worth paying 60 percent more for the bouch.
     
  7. Maarten28

    Maarten28 Active Member

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    My 12V battery is at 14.7-14.8V all the time while the car is on. I would not use that as an indication the battery is failing. If it is, my battery has been failing since at least 5 years.
    Did other settings go to default as well? Radio stations being forgotten?
     
  8. sam spade 2

    sam spade 2 Senior Member

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    When the car is "ON", you are not measuring the battery voltage but the charging system voltage.
    That tells you virtually nothing about the battery itself.
     
  9. Rebound

    Rebound Senior Member

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    First time I’ve heard that. They were first to have a Prius replacement battery, loads of Prius owners used them, and I never heard a complaint about them until now. But I don’t particularly care; I don’t work for them and if you’ve really experienced this I’ll take your word for it.
     
    Raytheeagle likes this.
  10. sam spade 2

    sam spade 2 Senior Member

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    Sometime around 2015, they had about 6 months to a year of a high initial failure rate; would only last about 6 months.
    That has been reported here.....several times.
    I don't remember seeing any complaints lately though......so I have no good data on how they last now.

    I DO have a problem with their marketing claims however.
    Whenever any company says that their product is orders of magnitude better than anything else IN THE WHOLE WORLD......I tend not to believe that.
     
  11. Grit

    Grit Senior Member

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    Optima was purchased by another maker and after that they stop manufacturing the spiral battery design & implemented ways to cut cost including quality of products, when that happened their reputation became average so it was a good company at one point.
     
  12. fuzzy1

    fuzzy1 Senior Member

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    That sounds quite good for your hot southern weather. While batteries with 84 or 96 month warranties (limited or restricted, never full replacement for that long) are available, the factory battery certainly doesn't fit that bill.
    The high voltage is not simply a matter of higher internal resistance. The charging system does adjust its set voltage according to the charge level it thinks is on the battery, starting at higher voltage when the charge is low, then stepping down when the charge is better. If your regulator never steps down on longer trips, that suggests the battery's age is showing. (Short trips may not be able to keep even a good battery charged well enough, Prii seem to have an issue with this.)

    My system voltage on a long trip today (on a battery just a couple months old) was just 13.5 V, i.e. well charged.
     
    #12 fuzzy1, Apr 19, 2019 at 12:28 AM
    Last edited: Apr 19, 2019 at 12:34 AM
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