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Key drains battery in 3 weeks

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Bjartmarr, Jan 2, 2017.

  1. Bjartmarr

    Bjartmarr Junior Member

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    My girlfriend has a 2010 Prius with two keys. Everything worked fine until about a year ago, when she started getting intermittent "key battery low" and "key not detected" messages while in her car. Touching the key to the power button makes the message go away for a while, but then it happens again an hour or a day later. Replacing the battery makes the problem go away, only to return after about 3 weeks. The dealer and I have both done the replacement, with different brands of battery.

    I know that storing a key near the car or near a phone can drain the battery, but key #1 is on her keyring attached to her wallet and is only near her phone briefly, and key #2 is 99% of the time on the coathook 100 feet from the car. The only thing I can think of is that both keys are often stored overnight on the coathook about 10 feet behind a TV: is that likely to drain the battery? A Honda smart key is also on the coathook sometimes; could that be the problem? It seems very unlikely that she is pressing the buttons by accident, especially on the spare key that only rarely gets used. I have suggested that the TV might be the problem and that she try storing the spare key in an alternate location; she just looks at me like that's a ridiculous suggestion, which it is.

    I store my phone and my 2013 Prius key in opposite pants pockets. Mom stored her 2005 and 2013 Prius keys in a jumble in her purse with her phone. Neither of us have had any problems.

    The dealer has inspected the car with his tricorder and claims there's nothing wrong with the car. Could he be mistaken? Is there a good way to check? Other than replacing the battery every 3 weeks, what's her next step?
     
    #1 Bjartmarr, Jan 2, 2017
  2. Former Member 68813

    Former Member 68813 Senior Member

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    Take it apart and clean it with pure alcohol. Use only fresh brand name batteries and avoid touching them with bare hands. Sweaty hands will deposit salt residue.
    I had this problem with cheap no brand batteries and the above steps mostly fixed it.
     
    #2 Former Member 68813, Jan 3, 2017
  3. WilDavis

    WilDavis Senior Member

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    Welcome to PriusChat! My 2009 Gen II started having intermittent problems with the SmartKeySystem about a year ago, doors not lock/unlocking etc. (see previous threads for details) - the long and short of it was that the 12V AuxBattery was on its last legs, I replaced the battery and all the SKS problems disappeared (well, the 12V battery was 6 or 7 years old! :eek:) - hope this helps - Wil
     
    #3 WilDavis, Jan 3, 2017
  4. David Beale

    David Beale Senior Member

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    It's possible the FOB is damaged. Still works but draws too much from the battery. I doubt it has anything to do with the car. The FOB may have gotten wet or damp or may have been "zapped" by static. Or it may have just degraded over time. She should have a second FOB. Try using that and see if the battery lasts. Mine lasts 3-4 years.
     
    #4 David Beale, Jan 3, 2017
  5. ETC(SS)

    ETC(SS) The OTHER One Percenter.....

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    Shoving it into an itty-bitty purse causing one of the buttons to be pressed........continuously........ is a possibility.
    I have a murse that used to do the same thing to my fob when I shoved a 1.5 pound polymer and metal device with a .451 in (11.5 mm) hole into it.

    I'm intrigued by the 100-foot coat-hook to car distance.....oh wait. You're in SoCal.
    Got it.
    Coats there.....aren't.

    One of the buttons on the fob may be sticking, which could be alleviated by @friendly_jacek 's excellent advice.
    Use one of those eyeglass cleaning pads and be careful with the alky.
    Unless it's a laboratory grade or says "everclear" on the bottle there will be a lot of water in it.
    It's not a problem per se, but you'll want to make sure that all of the liquid is evaporated before you put the battery back in.

    Separate the Yota and the Honda keyfobs, just in case they're not playing nicely together.

    Good Luck!
     
    #5 ETC(SS), Jan 3, 2017
  6. Former Member 68813

    Former Member 68813 Senior Member

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    on a second thought: GF with a prius, sounds like a keeper.
     
    #6 Former Member 68813, Jan 3, 2017
  7. Siward

    Siward Active Member

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    Last month, my Prius started giving me low keyfob battery warning messages due to the cold weather, so I decided to change it. I got curious and measured the dead coin battery's voltage with a multimeter.

    old coin battery voltage (purchased Aug 2015 lasted 16months): 3.003V
    new Eunicell coin battery voltage (purchased Aug 2015): 3.305V

    In summary, it took 16 months for the coin battery to drain .3V. I also leave my keyfob beside my cellphone. My keyfob is kept two floors away from the car.
     
    #7 Siward, Jan 5, 2017
  8. Bjartmarr

    Bjartmarr Junior Member

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    Thanks for the responses. I kind of doubt that the problem has to do with a dirty battery or dirty fob, since the problem happens with both fobs (including the one that does nothing but sit on the coat hook. I think the 12V battery has been replaced with a standard (non-AGM) car battery, but I'm not sure, so either way that could be the problem. She's not going to spend $200 on a new AGM battery just to fix the key problem, but I'll keep that in mind in case the car starts to exhibit other battery problems.
     
    #8 Bjartmarr, Jan 7, 2017
  9. bisco

    bisco cookie crumbler

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    does she live near a military installation? sometimes the fob will pick up unintended signals.
     
    #9 bisco, Jan 7, 2017
  10. Bjartmarr

    Bjartmarr Junior Member

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    There's a CIA listening post in the basement, but we're not supposed to know about that.
     
    #10 Bjartmarr, Jan 7, 2017
    bisco likes this.
  11. bisco

    bisco cookie crumbler

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    you just gave it away. but maybe they'll clear out now, and solve the problem.
     
    #11 bisco, Jan 7, 2017
    Mendel Leisk likes this.
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