1. Offline

    Dick Ginkowski New Member

    Member Since:
    Dec 17, 2009
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    Location:
    Pleasant Prairie, WI
    Your Vehicle Year:
    2010 Prius
    Model:
    II
    Better safe than sorry, so I wanted to find out how to replace the key fob battery before I need to do it. This is for the Denso 14ACX fob. It's easy -- just be gentle and slow.

    First, remove the metal key. Next to where it stows you'll see an opening in the plastic fob case into which the tip of the metal key fits perfectly. Insert the tip of the metal key and gently twist to pop open the cover. When it pops use the metal tip and glide it along the closed portion of the cover as gently as possible until the cover is completely off.

    Under the circuit board (lift gently) is a 1632 button cell. Remove and replace the button cell and circuit board and then reassemble the case as gently as possible. Voila!
    Econ, rebenson, fed123 and 4 others like this.
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    dtuite Silverback

    Member Since:
    Mar 25, 2010
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    Location:
    Redwood City, CA
    Your Vehicle Year:
    2010 Prius
    Model:
    II
    Holy cow! but you left out the part where the membrane falls off the piece with the plastic push buttons and the buttons fall on the floor.

    Like you said, the circuit board has the battery on the bottom so you have to pry the board out of its cavity to access the battery. And there seems to be a sticky piece of black rubber holding the circuit board down. I wish that were stickier, because that would make it easier to align the two pieces of the clamshell for reassembly.

    When reassembling, people should look for a boss on the inside of the non-button clamshell piece. That matches a round protrusion on the membrane and tells you you have the membrane in right.

    This is designed for owner maintenance? Leave yourself plenty of cussin' time.

    Don (who's grumpy about the battery going squat after 9 months, also.)
    2 people like this.
  3. Offline

    bob brown New Member

    Member Since:
    May 23, 2009
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    Location:
    flushing, ny
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    My 2010 model V key battery failed after only13 months and less than 5,000 miles. Is this normal? My 2004 model 9 lasted 5 years.
    1 people like this.
  4. Offline

    stream Senior Member

    Member Since:
    May 12, 2008
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    Location:
    Long Island, NY
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    I've had my Prius V 18 months (~18K miles) and have only used 1 of the fobs, and it's still ticking.
    1 people like this.
  5. Offline

    bob brown New Member

    Member Since:
    May 23, 2009
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    Location:
    flushing, ny
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    I just replaced the OEM Panasonic battery with an Enercell purchased at Radio Shack for $5.49 plus tax. Let's see how long this one lasts...
    1 people like this.
  6. Offline

    kithmo Couch Potato

    Member Since:
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    Location:
    South Yorkshire, UK
    Your Vehicle Year:
    2012 Prius+ MPV
    UK handbook says 1 to 2 years whether it's used or not, so check your spare.
    1 people like this.
  7. Offline

    bob brown New Member

    Member Since:
    May 23, 2009
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    Location:
    flushing, ny
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    My spare key works fine, but I bought an extra battery just in case...

    The key not in use should last longer than the one used. Lithiium batteries are supposed to have a long 'shelf' life--up to ten years?
    CaliforniaBear and laplante236 like this.
  8. Offline

    twittel Senior Member

    Member Since:
    Jul 7, 2010
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    Location:
    West End, NC
    Your Vehicle Year:
    2010 Prius
    Model:
    III
    I often keep my cell phone in the same pocket as my FOB and I've just got to stop doing that. I'm sure the bluetooth from cell and the RF from the FOB cause the battery to run down faster than normal. I also use a Palm Tungsten with bluetooth that I have to remember to keep seperate from my Prius FOB.

    Oh, I'm a slave to low level tech devices!

    Happy Motoring,

    Tom
  9. Offline

    esoniat Junior Member

    Member Since:
    Aug 13, 2009
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    Location:
    Marietta
    Your Vehicle Year:
    2010 Prius
    Model:
    II
    My battery is no longer detected in the back seat. I always throw my stuff in the back seat, so I'm guessing a battery is called for.

    As for the unused fob, I can think of reasons to replace both.

    You don't want the battery to fail and leak, it is much rarer now but can happen.

    You want the spare fob always available, not dead when you need it, so if it is 5 years before you change it that might not be the case.

    The fob may not be completely passive when out of range, noise etc may be waking it up so the battery life could be less than shelf life.

    I'm going to replace both each time.



  10. Offline

    tumbleweed Senior Member

    Member Since:
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    Location:
    Eastern Oregon
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    Has anyone tried the procedure on page 542 of the Owner's Manual? It tells how to start the car when the fob battery is dead. I have not tried it but I intend to when I replace my fob batteries. Might be very handy if you have a dead fob battery.
  11. Offline

    bob brown New Member

    Member Since:
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    Location:
    flushing, ny
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    I used it and it worked. BUT, perhaps there was a tiny charge left?
    Don't know if that would work if battery was completely dead. Perhaps I'll try removing it entirely and see if the fob will work that way. Although, maybe the battery dead or not needs to be in place for the car to 'read' through the dead fob?
    I feel more comfortable with the Generation II set-up where you had a receptacle to insert the entire fob.
    This makes me wonder...do all Gen III have the Smartkey? If not, where do you put the fob?
    1 people like this.
  12. Offline

    dtuite Silverback

    Member Since:
    Mar 25, 2010
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    Location:
    Redwood City, CA
    Your Vehicle Year:
    2010 Prius
    Model:
    II
    Is that about holding the fob up next to the start button? Yeah, that works. I did that when my battery crapped out. (see above.) There are two kinds of RFID tags. The kind we're talking about here gets its power by rectifying the RF that interogates it. It doesn't take much juice because it signals by shorting out its microwave antenna, which changes the amount of RF reflected by the chip in a coded pattern that the interrogating device can read.
    CaliforniaBear and tumbleweed like this.
  13. Offline

    tumbleweed Senior Member

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    Location:
    Eastern Oregon
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    Thanks Bob and Dtuite, it's good to know there is a backup procedure that works. Mine are both still working fine after 17 months so I'll see how long they will last.
  14. Offline

    macman408 Devil's Advocate General

    Member Since:
    Mar 21, 2010
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    Location:
    California
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    +1 to the removing the fob battery and trying the backup starting procedure. It requires absolutely zero charge, just like the proximity badge I wear at work to get in all the doors - I just have to hold the badge up to the sensor, and the badge is effectively powered by the sensor's radio broadcast. (Similar to the devices that let you recharge your cell phone by placing it on a special charging mat and not plugging it in - but lower power.)
    1 people like this.
  15. Offline

    bob brown New Member

    Member Since:
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    Location:
    flushing, ny
    Your Vehicle Year:
    2010 Prius
    Model:
    V
    Thanks, that's comforting to know. So I guess I won't go the the trouble of doing my 'test'.
  16. Offline

    fed123 Junior Member

    Member Since:
    Oct 24, 2007
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    Location:
    New Jersey
    Your Vehicle Year:
    2010 Prius
    Model:
    II
    Thanks so much for pointing out that one needs to lift the circuit board to find the battery. The manual at page 460 says nothing about lifting a circuit board. Until reading your post I was convinced that I had the wrong manual, the wrong key, or the wrong car.
    1 people like this.
  17. Offline

    kroketchie Junior Member

    Member Since:
    May 27, 2010
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    Location:
    new mexico
    Your Vehicle Year:
    2010 Prius
    Model:
    IV
    Thank you!
    Your directions are so clear! I was able to open the fob on my first try!

    Sincerely,

    Kroketchie
  18. Offline

    ItsNotAboutTheMoney EditProfOptInfoCustomUser Title

    Member Since:
    Jul 18, 2009
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    Location:
    Maine
    Your Vehicle Year:
    2010 Prius
    Model:
    II
    Thank you sir. Had to give it a good push to close it again but it's working.

    I've had the car for almost 3 years and inspection was 1 1/2 months old and it had 54 miles when I bought it. I've been getting key battery low messages for months but this morning the fob was finally dead.

    I used the key-fob-induction method to commute and followed these instructions when I got home to put in one of the pair of batteries I bought months ago.
  19. Online

    xliderider Senior Member

    Member Since:
    Apr 19, 2012
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    Location:
    Honolulu
    Your Vehicle Year:
    2011 Prius
    Model:
    Three
    Lol, at least the Prius is nice enough to give a message when the battery gets low. I just replaced the batteries in my Camry's key fobs when one just stopped working. No message. I'm glad I saw a post previously on this forum on holding the fob next to the Start button, because it works.

    Got my Eveready 1632 lithium batteries for $3 each at the drugstore.
  20. Offline

    Econ Member

    Member Since:
    Sep 4, 2009
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    Location:
    East of the Berkshires - MA
    Your Vehicle Year:
    2010 Prius
    Model:
    Five
    NO mine is going on 4 years. Still going strong.
    On my Lexus GS, the first battery change lasted six months. The replacements are not a good as the OEM battery. Least is seems that way. :( Perhaps your are pushing the buttons while in your pocket or something like that. I had the Prius keys in my pocket while in church and the horn started to blow. Honk Honk Honk. I had to get up and see where that was coming from and behold....... my lights were flashing. :( I usually Keep the key fob on a belt clip but this day I had them in my coat pocket. Like falling asleep on the tv remote! :)

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