12v battery ?? please help.

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Javierz0509, Jul 14, 2017.

  1. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

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    The cig lighter gizmo won't work when the car's off. I'd listen to @bisco: check it with voltmeter, car off, sat overnight.
     
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  2. bisco

    bisco cookie crumbler

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    tough concept to get across i guess.:rolleyes:
     
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  3. davids45

    davids45 Junior Member

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    G'day,

    My cig lighter gizmo does work with the car "on" in the two ways of turning it "on":

    1. Power = reads about 14+V (I push the blue start 'Power" button with my foot on the brake, so everything starts up)

    2. Accessory = reads about 12V (I push the start 'Power' button but without my foot on the brake - so only the accessories are powered up and are powered only by the 12V battery)

    The latter situation is useful to know the "stand alone" voltage of the 12V battery and, if watched for a while (say, 30 minutes?) with only the accessories as the power drain, how quickly the voltage is being lost. I don't know the Amp-hours rating of the battery nor how to predict how quickly it should lose charge when new, and when kaput. A monthly check of voltage loss under a standard time 'on' could be logged, I suppose, as a guide for those who like to do such things?

    Anyway, as a simple and cheap first-order approximation, I'd equate this Accessory-gizmo measurement to the leaving the battery overnight and checking the terminals by a multimeter, but without the hassle of reaching the terminals or removing the battery.

    If I found the Accessory-only voltage was less than 12V at Accessory-only start-up, or dropped quickly to 11V or less, then I'd think about taking it out, doing the bench test with my multimeter and then, in all likelihood, buying a new battery.

    David S.
     
  4. Javierz0509

    Javierz0509 Junior Member

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    i know a multimeter would be great, but with this device you have can you get a semi accurate measure of the voltage with accessories on only? let say like in the mornings?
     
  5. bisco

    bisco cookie crumbler

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    it's better for monitoring it down the line, compared to the day you install it.
     
  6. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

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    And if you want to get more serious: Solar BA5. They're around $70 IIRC.

    A better multimeter can set you back $100~200
     
  7. Sean Nelson

    Sean Nelson Active Member

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    You don't need a fancy multimeter to test battery voltage, pretty much anything will do. But of course note all the caveats on how to measure that voltage as discussed above.
     
  8. davids45

    davids45 Junior Member

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    G'day again JavierZ,

    Yes, I did it this morning (had to lean over from the driver's seat to read it) but it was 12.0V after a few seconds - it's mid-winter here so it's cold and things like batteries need to warm up a bit first - like me too, come to think of it.

    With the car being driven ('Power' now fully on), leaning over again this time stopped at a red light, I could see a steady 14.5V (presumably the feed from the High voltage battery charging the 12V battery). And for the first few minutes, a steadily rising 9.5C up to 10.0C as the car heater began to have an effect inside the car.

    I hope a casual monitoring of these voltages will warn me of any impending problems with the 12V battery. My 'c' is less than a year old so I'm not expecting any significant battery changes yet - maybe after three years or more as the climate here is fairly battery-friendly. And Toyota-original batteries have been good for about five years for the last four Toyotas I've bought.

    I really bought the 4-in-1 lighter-plug gizmo for the dual USB charging, the extra functions (volts, amps and degrees) were interesting to have.

    For the voltage precision required in checking a 12V car battery, I'm happy with my $10 Aldi multimeter. It's not 0.1V fractions of a volt differences that are crucial in checking the battery.

    I think a battery's in good nick if it is at least 12V after doing nothing for a while, say overnight, and is higher and holding, say 13+V, if just off a charging situation.

    And it does not rapidly lose voltage under load (drop under 11V say) - try Accessory-only-on mode and maybe turn the headlights on for a short while (10 seconds?). You would need to know, under these conditions, how quickly a good battery drained compared to a bad one, of course.

    Auto-electricians have calibrated gear to do this load test but I'm thinking of somethings simple the car-owner could do to easily monitor the battery over months if not years before needing to see the auto-electrician.

    Of course, a battery can just quickly fail 'mechanically' which monitoring won't warn you of.
    "Best laid plans of mice and Prius drivers oft gang aglay" (or something like that - Scottish is not my native tongue).

    David S.
     
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  9. jerrymildred

    jerrymildred Senior Member

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    No need to go anywhere near the battery (except on a Gen 4) to check the voltage. No tools required and only takes about one minute or less. If you check with a meter under the hood, you can check your oil while you're at it. And take a look at the coolant and brake fluid levels. And then you can use the multimeter for all sorts of things around the house.
     
  10. ztanos

    ztanos All-around Geek!

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    2012/Jan 2013 doesn't have the jump tab on the fuse box. This makes it significantly more difficult to check the levels from under the hood.
     
  11. Sam Spade

    Sam Spade Active Member

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    NOT a good conclusion.

    12.0 volts with little or no load indicates that the battery is about 50% DISCHARGED.
     
  12. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

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    With Solar BA5 you do have to connect directly to the posts. Connect at jump point and it'll complain. It tells you: voltage, Cold Cranking Amps and gives a rudimentary "verdict", course of action.
     
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