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    MissouriPrius New Member

    Member Since:
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    Location:
    Missouri
    Your Vehicle Year:
    2007 Prius
    I have been driving a 2007 Prius for 13 months with no problems. But, two days ago I got in the car and it would not start. The "check engine" light was the only light to come on. I had headlights and the key fob worked. I called the dealer and he had it towed. When I went to check on the car later that day, I was told it started as soon as they got it off the tow truck! I know the mechanic thinks I am nuts!! But that car would not start. The night before my husband had driven it and when he turned it off, he hit the power button a second time. So, I understand that that could cause the 12v battery to go dead, but would I have headlights? And why the "check engine" light?? And why did it start after being trucked to Kirksville? The mechanic would not let me bring it home--wanted to keep it over the weekend to see if it happens again. Any ideas???
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    efusco Troll Slayer

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    Your Vehicle Year:
    2004 Prius
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    Sounds pretty normal for a near-dead 12v. It had enough juice to do some functions but not all....after a little rest it was able to fire up the ECU for the start up.

    You really should get a little jumper box/tire pump combo so you can save yourself if this happens again...save you a lot of grief and time.
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    richard schumacher shortbus driver

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    Sounds like it needs a new 12V battery.

    In any case, try to train your husband to get in the habit of *always* locking the car, no matter where he parks it or for how long he intends to be gone. In most cases, if something is wrong (for example, a condition which threatens the battery, like not turning the car OFF) the car will give a long beep.
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    Bob64 Sapphire of the Blue Sky

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    tell the mechanic to check the 12v battery.
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    john12212007 New Member

    Member Since:
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    Location:
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    Your Vehicle Year:
    2007 Prius
    Model:
    I
    Yesterday I had a problem similiar to the one described by MissouriPrius and was forced to leave it in a walmart parking lot. Since this post was from over two years ago, I'm wondering if more people have experienced this and was the 12v battery the resolution. Instead of towing can I jump a Prius? Please advise. Thanks
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    jdenenberg EE Professor

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    The little 12v battery has about half the capacity of a regular car battery since it is not used to start the engine. It only needs to start the computers and a short burst of current to run a pump. Running the battery down does weaken it and if it can't hold a charge, you will need to replace it. The price should be under $200 at a dealer but some dealers will charge you excessively. An alternative is to get an Optima "Yellow-Top" battery (model 51 - not a 51r) and an adapter kit from ElearnAid (http://www.elearnaid.com/12vo1topraub.html) and either install it yourself or have any competent garage mechanic install it for you.

    You can jump a Prius, but be very careful. Connecting a 12v source backwards can cause several thousand dollars of damage to your Prius. It can either be jumped at the battery in the hatch area or at the "jump" point under the hood. To find the jump point (it is where you connect the positive cable) face the car and on the right near the firewall is a box with fuses. Open it and you will see a red plastic cap that can be opened by releasing a clip on the side. The "jump" point is under that cap. You connect the negative cable to any convenient metal part of the Prius body.

    Your Prius should NEVER be used to jump another vehicle.

    JeffD
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    john12212007 New Member

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    Location:
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    2007 Prius
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    Thanks JeffD. ls the Optimal battery and adapter kit you describe compatible with a 2007 prius, I noticed your's is a 2004? Also I thought the prius battery automatically got recharged from the kenetic tire moving energy produced when coasting along; I was originally sold on this model's regenerative breaking technology.
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    richard schumacher shortbus driver

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    The eLearnaid battery and kit fit all 2004-2009 Prius.

    The traction (high voltage) battery gets recharged both by the engine and regenerative braking, and the 12V battery gets recharged from the HV battery. This does not make the 12V battery immortal: abuse or age will kill it, the same as in any car.
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    pEEf Engineer - EV nut

    Member Since:
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    Location:
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    Your Vehicle Year:
    2008 Prius
    Model:
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    Yes, this is a very common problem. When it's cold out the 12v battery loses capacity, so if it is marginal it will usually fail to start on a cold morning, but if left to sit will start later in the day as the sun warms it up a little. I've seen the 12v batteries last only a few years for some people, while others go for over 4 years. If your battery is over several years old, it's best to check it, as there is no warning in the Prius, it simply fails to go ready one cold morning. (with a red "triangle of death") Whereas in a normal car it will start cranking slow to let you know it's on it's last legs.

    There are many threads here on how to use the MFD to perform a cursory check on your battery. Search is your friend!
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    BAllanJ Active Member

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    Location:
    Kingston Ontario
    Your Vehicle Year:
    2009 Prius
    Model:
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    I wonder if you can do to these little batteries what I used to do on very cold mornings if the battery couldn't quite start the engine... I turned the lights on for a minute or so. The current draw through the internal resistance of the battery warmed it enough that it could then provide enough current for the start if you then turn the lights off. Not recommended if you've cranked enough to actually deplete the battery.

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