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12V battery dying?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by HoosierPrius, May 4, 2014.

  1. HoosierPrius

    HoosierPrius New Member

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    Hi! Our 2009 has 75K on it and I believe still has the original 12V. Two nights ago I parked after driving for a couple of errands and it put on a terrific light show, tried to refuse my shutting it down and in the end gave me a message about a tranny issue, saying to be sure to park it somewhere flat. My driveway is not at all flat, so I put the parking brake on, as I always do, and proceeded to panic that the car was going to be dead in the water.

    Got on here and see a lot of talk about this being a warning that the 12V is about to die. Fair enough, but now it is acting totally normal. Should I assume it is going to leave me stranded and replace the battery, or call that event a fluke? And how tricky is replacing the 12V? Clearly not as simple as the under the hood battery swap, but a decent DIYer could handle it as a relatively quick repair?

    Thanks, this forum is SO useful. The one thread I could find with an easy check for battery charge seemed to be showing a Gen 1 screen, and I cannot see how to get there on my Gen 2. Not to mention my new fear of draining the battery in ACC mode...
     
    #1 HoosierPrius, May 4, 2014
  2. bisco

    bisco cookie crumbler

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    exactly right about changing the battery. give it a test first, maybe it was just a fluke. shut it down and test it in the morning and report back.
     
    #2 bisco, May 4, 2014
  3. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Yes, you should assume the car will leave you stranded and replace the 12V battery now.

    It is not very hard to replace, you will find many posts about that. Try not to lose the bolt that attaches the traction battery vent to the right rear fender. It is very easy to drop that into the 12V battery compartment. Use some Vaseline or other heavy grease in the socket to help retain the bolt in the socket until you've screwed it in.
     
    #3 Patrick Wong, May 4, 2014
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  4. HoosierPrius

    HoosierPrius New Member

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    Thanks, all. Not a bad problem all things considered. A few weeks ago we tried a DIY to reduce the condensation in headlights with success, so I will just be thankful we didn't drop hundreds if dollars on new assemblies and fork over some cash for a new 12V. Rather not be stuck!
     
    #4 HoosierPrius, May 4, 2014
  5. cyberpriusII

    cyberpriusII Prodigyplace says I'm Super Kris

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    Did it in December (?). If you find the thread I started, (try searching for my posts around then), it will tell you all you need.
     
    #5 cyberpriusII, May 4, 2014
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  6. dorunron

    dorunron Senior Member

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    Try reading my signature file below this post. In my signature you will see four links.

    The first two will help you "test" the battery AND install a "NEW" battery.

    You can DIY. And yes, you probably need a new battery based on everything you said. If you don't change it soon, it will eventually leave you stranded. Run the test mentioned in my sig file. Do it in the morning before you drive the Prius. Post back with all voltage levels if you can.

    Ron (dorunron)
     
    #6 dorunron, May 4, 2014
  7. HoosierPrius

    HoosierPrius New Member

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    Husband already replaced it, so fingers crossed!
     
    #7 HoosierPrius, May 4, 2014
  8. dorunron

    dorunron Senior Member

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    You ought to be good to go then. What brand of battery? Yellow Top, Exide, OEM?

    Ron
     
    #8 dorunron, May 4, 2014
  9. HoosierPrius

    HoosierPrius New Member

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    I honestly have no idea. I called around for a yellow top, was told by o'reilly's that they carried them. Sent husband and they sold him something else, apparently the yellow top they had was not right for the prius. He swapped it out in the parking lot, so never saw it! Hence the fingers crossing. :/
     
    #9 HoosierPrius, May 5, 2014
  10. dorunron

    dorunron Senior Member

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    No problem. I completely understand. What is important is that your Prius is back on the road.

    Best of luck to you.

    Ron
     
    #10 dorunron, May 5, 2014
  11. Classic Car Guy

    Classic Car Guy Active Member

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    This might be the right threading for the 2007 12 volt battery replacement. Any recommendations for a replacement that will fit and has a bit more capacity than the stock. I drained the battery twice in 2 years. The last time is when the alarm went on new year. Other than that its back to normal. But I'm afraid I might be replacing it down the road. It feels like the original battery has a very small capacity. Any takes? name and size of battery? Thanks,
     
    #11 Classic Car Guy, Jan 5, 2021
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