Checking 12V Battery

Discussion in 'Gen 3 Prius Main Forum' started by ednorton, Nov 15, 2021.

  1. ednorton

    ednorton Junior Member

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    Hello,
    Just checked my 12V battery. I checked it through NAV and had 12V as reading. Then I checked the front jumper and at the battery terminal, both readings were 12.6V. Why do I get nearly a half V difference through the NAV? Thanks!
     
  2. bisco

    bisco cookie crumbler

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    you lose voltage through wiring, fuses, relays, circuit boards, connections and etc.
     
  3. bisco

    bisco cookie crumbler

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    also, did you turn the car off to check it at the jump point? if so, most of the load would be gone.
     
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  4. ednorton

    ednorton Junior Member

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    I just checked the NAV which reads 12V, then just checked the jumper with car still on ,12.2V. Also checked at jumper with engine on, headlights and a/c on with reading of 14.98V.
    Does it look like battery is still good? Thx
     
  5. rjparker

    rjparker Senior Member

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    Checking with the system in Ready just reads the charging voltage from the inverter's dc to dc converter. A decent method is to measure with a meter first thing in the morning without starting the car. Less than 12.2v is weak but then it would be prudent to measure parasitic draw if the 12v battery is less than four years old. Even better is a free load test of the battery at most auto supplies.

    By the way, cheap meters like the "free" to $7 meters at Harbor Freight can read high. The voltage monitoring in a Prius is generally more accurate.
     
  6. bisco

    bisco cookie crumbler

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    looks like it is still in decent condition, how old is it?
     
  7. ednorton

    ednorton Junior Member

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    It's the original battery!
     
    #7 ednorton, Nov 16, 2021
    Last edited by a moderator: Nov 16, 2021
  8. ednorton

    ednorton Junior Member

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    I'm just cautious now and checking numbers now, since I left trunk light on for at least a week.
     
  9. rjparker

    rjparker Senior Member

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    It needs a new battery. A ten year old original is guaranteed to strand you soon.
     
  10. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Oh hell, yeah. And if you're serious about wanting to "test" a 12 volt battery, look into electronic load testers. Reading the battery's voltage through the car display, and even just reading just the voltage with a multimeter, isn't that accurate.

    Solar is the brand I'm familiar with, but there's lots of options:

    upload_2021-11-17_11-37-20.png

    Ancel's another good name I think; see a lot on Amazon.
     
  11. sam spade 2

    sam spade 2 Senior Member

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    Say WHAT ?
    I've owned about a dozen of the little red meters from HF over the years and NONE of them has ever has a significant error.
    But to be fair, after MANY years of use and abuse, a couple of them did fail completely but then the readings were WAY off so that it was obviously not right.

    AND.....I don't remember anybody here EVER reporting that the "voltage monitoring" reading that you see in a Prius is anywhere close to being accurate. Never.

    It looks to me like you have it exactly backwards.
     
  12. ednorton

    ednorton Junior Member

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  13. ednorton

    ednorton Junior Member

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    I know I'm taking a chance, with a battery so old, but I'm curious as to how much longer it can last. Its like seeing your gas gage on "E" and seeing how many more miles you can get out of it!! Didn't Kramer do that on Seinfeld? Does anyone know if I would eventually get some kind of caution light in advance? But maybe the smartest thing to do is get that battery tester, or buy new battery, but I ain't that smart:)
     
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  14. bisco

    bisco cookie crumbler

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    i did the same. it was reading static 12.6 right up until the day it died, stranding me only 4 miles from home fortunately.
    i'm hoping to get 20 years out of my '05 dakota battery!

    what's life without a little risk?:p
     
  15. sam spade 2

    sam spade 2 Senior Member

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    You give yourself too little credit.
    The fact that you are asking the questions that you ARE sure looks like you KNOW what the answer is but are just contemplating "tempting fate".
    You likely will be sorry if you do.

    Unlike a conventional car where you might notice dim lights or the starter turning over slow, the signs of a battery getting weak in a hybrid are much more subtle......or may not happen at all until it just refuses to "start" at some random place and time.

    Owning a battery tender is a good thing. Using it regularly can extend the life of an old battery.
    BUT that also almost guarantees that the ultimate total failure will occur at some place AWAY from home when it is most inconvenient.

    Show us that you really ARE that smart; get a new battery or at least get your old one tested.
    Unless you really enjoy surprise adventures. In that case, just keep going......until it doesn't.
     
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  16. jack curry

    jack curry New Member

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    Don't let the battery go completely dead. If it is you can't open the back door to get to the battery. Very inconvenient.
     
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  17. ednorton

    ednorton Junior Member

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    Ok, guys, you convinced me, and I don't want my wife giving me an earful if we get stuck somewhere!!!! Ordering one now.
     
  18. ednorton

    ednorton Junior Member

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    I guess I'll go with Toyota's True Start battery, does everyone agree with this choice? Thx for advice!
     
  19. ASRDogman

    ASRDogman Senior Member

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    It's hard to go wrong with a Toyota part. (y)
     
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  20. jerrymildred

    jerrymildred Senior Member

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    That is an excellent battery. It's basically the same battery that has been lasting you over twice as long as the average battery.
     
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