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Level 3 12 volt battery test

Discussion in 'Gen 3 Prius Technical Discussion' started by lenjack, Oct 19, 2019.

  1. lenjack

    lenjack Active Member

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    What is the best way to test the 12 volt battery on a 2010 level 3, with 138,000 miles? Car works perfectly, but overall mileage has dropped in last few months from 51 to 47. No changes in driving characteristics or tire pressures or drivers. The 12 volt was replaced about 4 years ago with an oem. I have a digital meter?
     
  2. bisco

    bisco cookie crumbler

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    best way is to take it for a free load test at an auto parts store.

    second best is to put the voltmeter on the jump point first thing in the morning with the car stone cold, then turn the headlights on and watch the voltage drop over a few minutes

    how about ambient temp and heater use? i know this isn't your first rodeo.
     
  3. bisco

    bisco cookie crumbler

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    otoh, there are so many things that affect mpg's. how many miles on her, and what non official maintenance have you performed?
     
  4. lenjack

    lenjack Active Member

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    Many thanks. Ambients are 48 to 72F, and temps set at auto, 72F. The stone cold reading with the car off? The headlight reading with the car off? What should the readings be, if all is well?
     
  5. lenjack

    lenjack Active Member

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    Mileage is in my post. Oil changes at 10k miles. Tires have 25k miles at 39-37. Other maintenance is minimal. Mileage changes as mentioned are recent.
     
  6. bisco

    bisco cookie crumbler

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    you haven't done the major maintenance at 100k and 120k?

    egr circuit?

    throttle body and maf?
     
  7. lenjack

    lenjack Active Member

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    I have not. Is this the price I pay? If so, I admit my mistake. What would that maintenance probably cost at my dealer? If it's a 12 volt problem, I can fix that.
     
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  8. bisco

    bisco cookie crumbler

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    100k is a fluid, 120k is plugs, they might be an issue. hard to put a price on it. i would call around, don't trust one dealers price.
    air filter is important, cabin filter helpful.

    egr, throttle body and maf are not in the recommended services, but can be problematic.
     
  9. lenjack

    lenjack Active Member

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    Air & cabin, I do myself. I will do them.
     
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  10. bisco

    bisco cookie crumbler

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    i just check them and tap them out, unless they are really bad
     
  11. PriusCamper

    PriusCamper Senior Member

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    Here's the #1 ---> 12v battery test comment I've read on this site:

     
  12. StarCaller

    StarCaller Senior Member

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    how you gonna 'fix' your 12v battery ?
     
  13. lenjack

    lenjack Active Member

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    "how you gonna 'fix' your 12v battery ?"

    By replacing it.
     
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  14. lenjack

    lenjack Active Member

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    What should the 12 volt read, after overnight, dead cold, with the car off, and what should it read with the car on after running for a few minutes?
     
  15. bisco

    bisco cookie crumbler

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    it's not a set value. they are 13v new and decline with age and use. around 12.4 is borderline, but it also depends on the load value. the computers expect a certain voltage, and that is after the load and wiring drop.

    a 4 year old battery in your climate is not a likely suspect, unless it has ever gone dead and had to be jumped/charged.
    but a defect is always a possibility.
     
  16. StarCaller

    StarCaller Senior Member

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    my yellow optima never ever showed more than 12.7v after sitting overnight, so after 4 years I assume that's a good number to go by /
     
  17. SuperchargedMR2

    SuperchargedMR2 Diehard Rams Fan

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    I want to replace the 12v battery on my wife's 2010 Prius. It still has the OEM battery and it's been okay but I don't want to wait for it to fail. What are good choices for replacement? OEM again? Optima? Other brand?
     
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  18. PriusCamper

    PriusCamper Senior Member

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    For perspective here's some comments on the not really exactly 33amphour Optima:

    YellowTop_Criminals.png
    Currently I've been recommending a $97 ---> 55amp hour battery on Ebay... I don't think anyone can beat this one. And as sketchy as ordering a 12v battery online can be, both me and my buddy are quite pleased with our purchase: 12 Volt (12V) 55 Amp (55Ah) VRLA AGM Sealed Lead Acid Battery 55 AMPS HIGH CAP | eBay
     
  19. ASRDogman

    ASRDogman Senior Member

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    Holy crap! 10 years on the original??? Well now you MUST replace it, because you talked about it!
    It will for sure fail now! :)
    I was lucky with the Prius I bought. The man replace the battery with a Toyota battery a few months before
    I bought it. Well, he had Toyota do it. I've had no problems with it.

    When it comes time to replace this one, I will probably get another Toyota battery.
    You could probably use a UPS battery in it! :)

     
  20. TMR-JWAP

    TMR-JWAP Senior Member

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    That's an interesting battery, especially since I've been keeping an eye out for one to install in my sons car.
    Couple questions for you about it:
    1. It shows as having button connectors that need a threaded stud type post added. Were you able to find a studded JIS post? If not, what did you use? Could probably get a studded standard post and just turn it down on a lathe if needed. Hmmm. wonder if there would be a market for that? (always on the lookout for another niche side gig, lol)
    2. Did it mount cleanly in the OEM holder assembly and did the floor plate go back in place properly?
    3. Does it have the vent tube/hole? Looks like it does in the photo of the + terminal. Looks like it may be on the passenger side of the battery instead of the forward side. Any problems making that connection work?
    4. Their description says needs replacing every 2-4 years. Seems short but that may be due to their expected usage. How long have you had it and have you done any capacity testing to see how it's holding up? Something like a monthly/quarterly test using an electronic battery tester?