Need to replace 12V battery?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by macmaster05, Mar 2, 2011.

  1. macmaster05

    macmaster05 Senor Member

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    My mom has an '06 Prius w/ 45k miles on it. I started suspecting her 12V battery was low when her car starting to beep each time she shut it off. She also tells me she only gets 49 mpg now, which is the same as me, and I drive pretty aggressively. She used to always get much better mileage than me.

    Today she went to a mechanic to test the battery. He said it was at 8V. She doesn't know whether to take his word for it. After all, he mentioned that one symptom would be a difficult/slow startup. That, however, is not one of her symptoms, and I've never heard of that happening.

    So does the battery need to be replaced? Are there any other DIY tests I could run? Should she get the battery replaced immediately, soon, or later? She thinks it can wait. I think it needs to be replaced ASAP. But I could be wrong. Thanks!
     
    #1 macmaster05, Mar 2, 2011
  2. seilerts

    seilerts Battery Curmudgeon

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    #2 seilerts, Mar 3, 2011
  3. macmaster05

    macmaster05 Senor Member

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    No the smart key fob battery isn't weak. That's what I thought at first to, so I had her using the 2nd smart key. Still beeps.

    Thanks for the link.
     
    #3 macmaster05, Mar 3, 2011
  4. seilerts

    seilerts Battery Curmudgeon

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    Would it make sense that the batteries would die at the same time? Do fob batteries die due to usage or shelf life? I have an '05, only one key, and had to replace the battery about 7 months ago. I think she's due. It can't hurt, these things are just a few bucks.
     
    #4 seilerts, Mar 3, 2011
  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    Unlike almost every other car the mechanic sees, the Prius never turns a starter motor with the 12 v battery, so a weak 12v will not make starting sound slow.

    Yes replace the 12v battery now. One of the few 'self inflicted' things that can go wrong on a Prius is badly jump starting the car, which can cost thousands.

    Only two batteries really make sense:
    1) Your Toyota dealer sells the same battery you have now, for about $135

    2) elearnaid sells a Optima Yellowtop with a kit to make it fit in the otherwise incompatible Prius for $180.

    The Optima is a 'better' battery, if you plan to keep the car forever, or at least 5 more years.
    http://www.elearnaid.com/12vo1topraub.html
     
    #5 JimboPalmer, Mar 3, 2011
    1 person likes this.
  6. Mike Dimmick

    Mike Dimmick Active Member

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    If it's as low as 8V - and it can be - the car will still boot, but you'll see the warning triangle appear on every startup, with a long beep rather than the usual double-chirp.

    Trust me, this has been happening to me for the last two weeks!

    If the battery really is this low, the MFD won't turn on in ACC and IG-ON modes. I've watched it go 8.7...8.6...8.5...8.4 in the Vehicle Signal Check diagnostic screen, then turn off.

    I have now replaced it with an Optima type YTS 2.7J, which I'm going to start a new thread about.
     
    #6 Mike Dimmick, Mar 3, 2011
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    I knew it was only a matter of time ;)
     
    #7 Mendel Leisk, Mar 3, 2011
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