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12-volt battery problem

Discussion in 'Gen III 2010+ Prius Care, Maintenance and Troubles' started by sphawk, Mar 23, 2011.

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  1. sphawk

    sphawk New Member

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    Location:
    Kansas City, MO
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    I drive a 2010 Prius V, 8500 miles. We took a first long (non-commute) trip in the new Prius and, of course, encountered the first problem with this car 500 miles from home. To deliver the punch line first, my problem was at least on surface solved with replacing the 12-volt battery. I need to know how this happened, though. I'll recount the circumstances.

    After 500 mile drive, parked car. 65 degree ambient temp. Two hours later, went out to remove some items from rear hatch, and discovered that the all exterior and interior conveneince lights were out but the display panel on dash was on -- as if I had not shut down the system when I left the car earlier in the evening (I've never failed to do this before). Car started fine, and I moved it to a more convenient parking spot (very short drive). Two days later, 65-75 degree temperature, car started great, and drove the Prius 40 miles, parked, and back 40 mies to a parking garage while we ate dinner. After my earlier experience with the display being on, I was explicitly careful to turn off the car with the power button, then turn off the headlights, then lock. When we returned to the car 2 hours later, the headlights, fog-lights were all on, car was locked! Strains of Twilight Zone theme music ...

    Car started perfectly, drove 2 miles, then I parked: made certain car was turned "off" and lights were out. When I came out an hour later, park and fog lights were on, faintly as I recall (though no headlights) and the car would not start up. Clicking noise upon hitting start button, lights flickered at frequency of the "click," then all was dead: no interior lights, no ability to lock electronically, or to open back hatch from outside. Briefly I did read the infamous "Parking brake" message, directing me to put on, then off, the parking brake and park on a flat surface -- a tall order with car dead!) Rather inconvenient!

    Towed (dragging car onto a flat-bed truck, as front wheels were locked and could not be released)to Toyota dealer. Toyota dealer replaced the 12-volt battery, did comprehensive tests, found no other problems. We drove the 500 miles home yesterday, and the car seemed to worked perfectly.

    But why and how did this happen? How would a failing 12-volt battery cause headlights to go ON? Why, even if I did (and I don't think i did) leave lights on, wouldn't the lights just go out after a minute or so delay? Is there something different I should do -- trickle charger, install different (Optima?) battery, get checked for early-Alzheimers onset?

    I make no claims for being an auto-techie, but would practically like to know how this occurred and assure it never happens again!
  2. ksstathead

    ksstathead Active Member

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    Location:
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    Your Vehicle Year:
    2010 Prius
    Model:
    III
    None of what you described were short trips. Curious do you do a lot of very short trips? How old is the car?

    I got a batteryminder to occaisionally freshen the 12V since we make short trips often, and I check it sometimes with a digital multimeter.

    Odd behavior such as your car's failure symptoms is not unique when Prius 12V dies. I'm pretty sure you never left the lights on during the failure sequence described.

    Ours has 21M miles over 15 months with no such problems, but we fit the profile for an early 12V failure.

    Suggest you spend $10-20 on a digital multimeter and keep an eye on the 12V condition. There could be an excessive drain on it that will ultimately require diagnosis and warranty replacement.

    Will watch this thread with interest. Good luck, neighbor.
    1 person likes this.
  3. Mendel Leisk

    Mendel Leisk Senior Member

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    Location:
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    A 12 volt in good condition should show about 12.6 volt, or higher.
  4. tumbleweed

    tumbleweed Senior Member

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    Location:
    Eastern Oregon
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    Those are pretty weird symptoms but, as mentioned above, low 12V batteries can cause strange things to happen. I don't think you caused this problem, there have been quite a few people on here that have had bad 12V batteries in their 2010 Prius.

    There is one thing you might not be aware of with the auto-off headlights. If you turn them on after you have opened the door they will not turn off automatically, they must be on when the door is opened with the car turned off.

    If my 12V battery goes dead or reaches 4 or 5 years of age I will replace it with an Optima, unless something better comes along in the meantime.
  5. Den49

    Den49 Member

    Joined:
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    Location:
    Maryland
    Your Vehicle Year:
    2010 Prius
    Model:
    IV
    One thing to consider before replacing the Prius battery is that it is a relatively small capacity battery and it is easier to deplete its charge than a non-hybrid car battery. The Prius may also be more sensitive to a low voltage battery causing a no start condition.

    Below are the instructions from Toyota for checking Prius auxiliary battery voltage. Note that the first step is a NOTICE to recharge the battery and check it before returning the vehicle to the customer. For whatever reason, a battery may run down to less than the required starting voltage, but is still a good battery and only needs to be recharged.


    1. CHECK AUXILIARY BATTERY VOLTAGE

    NOTICE:
    If the battery is fully depleted or "READY" does not light up, recharge the battery. Check the battery again before the vehicle is returned to the customer.

    (a) Check the battery for damage and deformation. If severe damage, deformation or leakage is found, replace the battery.
    (b) Check the voltage.
    (1) Turn the power switch off and turn on the headlights for 20 to 30 seconds. This will remove the surface charge from the battery.
    (2) Measure the battery voltage according to the value(s) in the table below. Standard Voltage:

    Tester Connection
    Condition
    Specified Condition
    Positive (+) terminal - Negative (-) terminal
    20°C (68°F)
    12.5 to 12.9 V
    1 person likes this.
  6. sphawk

    sphawk New Member

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    Location:
    Kansas City, MO
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    My trips are prevailingly 30-35 mile commutes within KC metro area 2x daily. The car has accumulated about 8500 miles since November 2010. There are occasional shorter trips, 2-3 miles, but seldom just a few thousand feet, if that is the question. I have searched my recollections for anything that would constitute an unusual drain on the battery, and found nothing. I have no add-ons or plug-in accessories. A battery-minder would be affordable, and I think I have an inexpensive multimeter around someplace -- I'd just have to figure out how to use it. It would be very interesting to chart the draw under various conditions and compare to the standards various responders have posted.

    I feel better having read these various posts. I think there must have been something faulty with the original battery, rather than a fault from my brain having suffered a battery! Thanks to all!
  7. sphawk

    sphawk New Member

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    Is the "ready" icon a meaningful read on battery charge status?
  8. ksstathead

    ksstathead Active Member

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    Model:
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    No, other than that it had enough juice to boot the computers?

    It will keep working well below the voltage that you'd like it to be.
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