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    Tom blue ribbon blue New Member

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    Location:
    Wisconsin
    Your Vehicle Year:
    2010 Prius
    Model:
    Three
    I had been having problems with my Pruis III ready light not coming on for the last year. I had tried various options and after several trips to two dealers I finally insisted that they check the voltage on the 12v battery. Well, what I had suspected all along was a defective battery was causing the problem. They replaced it under warranty and all has been well. If you have had this annoying experience, make sure that this is the first thing the dealer checks.
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    jdcollins5 Senior Member

    Member Since:
    Aug 30, 2009
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    Location:
    Wilmington, NC
    Your Vehicle Year:
    2010 Prius
    Model:
    III
    Yes, there are multitudes of threads on here about all kinds of weird problems being caused by the 12V battery. The Prius 12V battery is much smaller than most since it does not have to start the ICE. This is done by MG1.

    All the 12V battery is required to do is to power electronics in ACC or IGN-ON modes and to power up the various ECU's and pull in the HV battery relays on Power on and Ready.

    All it takes some time is to leave an interior light on overnight to discharge the battery. Once discharged it may recover when recharged but it will probably fail in a short amount of time.
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    Mendel Leisk Senior Member

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    Location:
    Greater Vancouver, BC, Canada
    Your Vehicle Year:
    2010 Prius
    Model:
    N/A
    A near-new car can have a near-dead 12 volt battery, if it's been sitting idle on the dealer's lot for sometime. That was the case with us, our car had been on the lot for multiple months. The 12 volt was replaced during dealer prep, no problems since.

    I'd suggest to get a digital multimeter. Then you can keep tabs on it yourself. A trickle charger hooked up regularly might be beneficial too, or for instances where there was a partial drain, say due to a dome light left on.
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    spiderman wretched

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    Location:
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    Your Vehicle Year:
    2010 Prius
    Model:
    II
    Hey JD, was it determined that the SGII's voltage gauge was very accurate for the Prius?
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    Tom blue ribbon blue New Member

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    Location:
    Wisconsin
    Your Vehicle Year:
    2010 Prius
    Model:
    Three

    Thanks for your answer. Thank is exactly what happened. I left the dome light on for two days and even though I jumped started the car the battery never fully recovered.

    Any suggestions for a tickle down charger and when should it be used?

    Tom
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    Tom blue ribbon blue New Member

    Member Since:
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    Location:
    Wisconsin
    Your Vehicle Year:
    2010 Prius
    Model:
    Three
    I appreciate your technical insight to my battery problem. I had left the dome light on for two days and the battery never recovered. I seems to be easy to do if your not paying attention and forget you turned it on.

    Tom
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    David Beale Senior Member

    Member Since:
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    Location:
    Edmonton Alberta
    Your Vehicle Year:
    2012 Prius
    Model:
    N/A
    My Scangauge voltage readout seems to be accurate.

    I purchased a "Battery Tender". They're pretty good, and come with two sets of "pigtails" for the battery connection cable. One has clips, the other ring terminals. I used the one with ring terminals on Pearl, connecting the positive to the "jump point" by removing the nut and putting the ring terminal on the bolt then putting the nut back on. Be careful when doing this if you don't disconnect the battery as the boost point is live at all times (well, until you blow the 100 Amp fuse ;) ). I use the other "pigtail" on the FJ Cruiser. The FJ tends to sit unused for long periods in Summer, while Pearl may sit unused for longish periods in Winter.

    The "Battery Minder" is also supposed to be good, though I haven't tested it myself.
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    szgabor Active Member

    Member Since:
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    Location:
    Oceanside NY
    Your Vehicle Year:
    2012 Prius
    Model:
    Two
    Mine is .... I measured the turn-off voltage by a multimeter for several minutes after shutting the car down ... ScanGauge showing the voltage for about 30-40 second for that time it was the same as my elchepo chinese multimeter ... well the scan gauge shows 1 decimal only but at that range it was pretty close to what I was measuring ....

    When the car is on it is hard to measure 'battery voltage' what you can only measure is the charging voltage of the inverter(well DC/DC converter) puts on the battery that also matches pretty well with multimeter ... again if 1 decimal an issue in that range yes there is some deviation but within that scangauge (at least mine) was accurate.
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    Speedracer New Member

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    Location:
    Nagoya, Shanghai
    Your Vehicle Year:
    2011 Prius
    Model:
    N/A

    Dear Toyota you have problem!

    Past few weeks my car show 12v battery warning when ever start the car. But yesterday (June 3rd) get worse.
    So drive down to dealership (not bought a car from but same company)and let them diagnostic the problem.
    Half hour later dealer personal advice me they would like to keep my car over night. So today I called the dealership which I bought my car and I told them fix the problem or I want money back.

    This is pity my car is less than year old and this problem.
    Also make wired noise and brake has own its mind.

    Well no call from dealership today and lucky yesterday dealer put me loaner.

    My confidence has lost with Prius...

    As everyone know before Type 3o I had Type 20. My Type 20 brake failed high way exit and almost involved an accident.

    So now I just wait phone call from dealership.
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    friendly_jacek Senior Member

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    Oct 3, 2010
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    Location:
    southeast US
    Your Vehicle Year:
    2010 Prius
    Model:
    II

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