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Which battery is dead?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by English Jack, Feb 12, 2011.

  1. English Jack

    English Jack Junior Member

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    Location:
    Daytona Beach, Florida
    Vehicle:
    2007 Prius
    I have a 2007 Prius which I bought new. Due to driving to New Jersey and back to Florida at least four times and more a year I have about 65,000 miles on the clock. A few months ago I decided not to drive it just to try and keep the mileage down.

    I got in it a few weeks ago and it was dead; no lights, no power at all and rear door obviously would not open. I got it open and jump started it using the small 12-volt battery in the back. Drove it around for half an hour or more and it seemed fine. I used it for a few days and then left it again for a few weeks. Then last Sunday I got in it again and the same thing; no power, etc. I put the 12-volt battery on charge and left it. My charger said the battery was fully charged so I got in but it still would not start; no lights, etc. I again started it with a jump start.

    As a complete and utter dummy I would like to know if it is the 12-volt battery or the big hybrid driving battery that actually goes dead. When the gasoline engine starts is it the 12-volt or the hybrid battery that starts it? I realize that these seem like dumb questions but I have got used to jumping in the car, starting it and driving it without actually thinking about it.

    I would greatly appreciate any answers that you may be able to give me and I thank you in advance.
     
    #1 English Jack, Feb 12, 2011
  2. ksstathead

    ksstathead Active Member

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    The HV spins the ICE to start, but the 12V must first power up the ECUs. So both are necessary and neither is sufficient alone.

    The 12V is the one that is usually the culprit. A dead HV would have other symptoms long before it was unable to spin the ICE at startup.
     
    #2 ksstathead, Feb 12, 2011
    1 person likes this.
  3. seilerts

    seilerts Battery Curmudgeon

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    These cars don't like to sit. In fact, this is one of the lowest emitting, highest efficiency transportation options available, so the greatest cost/benefit comes from making the Prius be the vehicle that you use whenever a bicycle doesn't work. Replace your 12V battery and drive your Prius as much as possible. If you do let your car sit for weeks at time, you really should use a charge maintainer (Battery Minder) on the 12V, otherwise it will sulfate and not hold a charge, which is what has happened to you.
     
    #3 seilerts, Feb 12, 2011
    1 person likes this.
  4. Mendel Leisk

    Mendel Leisk EGR Fanatic

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    Vehicle:
    2010 Prius
    Model:
    Touring
    With the 2nd gen, isn't it constantly checking for a FOB in the vicinity, and consequently incurring a parasitic drain on the 12 volt battery? I believe for extended down-time, there's a button on the underside on the dash you can push, that turns this behaviour off, and better preserves the 12 volt battery.

    If you're going to have the car sitting for some time, maybe also look into intelligent chargers, one that you can leave hooked up constantly (assuming you're garage storing, or at least within range of an extension cord). Barring that, a solar charger with the collector on the dash might help.
     
    #4 Mendel Leisk, Feb 12, 2011
    1 person likes this.
  5. firepa63

    firepa63 Former Prius Owner

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    It's your 12v battery ... replace it.
     
    #5 firepa63, Feb 12, 2011
    1 person likes this.
  6. English Jack

    English Jack Junior Member

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    2007 Prius
    To all of you who took the trouble to reply to my "dumb" questions a BIG THANK YOU.
     
    #6 English Jack, Feb 15, 2011
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