What the heck is the deal with the 12 V batteries?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Ozy, Jan 16, 2019.

  1. Ozy

    Ozy New Member

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    I have a Prius 2005 which is not driven very often because it isn't my main car anymore. The car tends to die on a regular basis even though it's being driven approximately once a week (short drives). I have changed the battery a couple of times and the problem recurs after a short period. Last week I found the battery dead and had AAA come by and jump start it. I then drove the car around for about 20 miles and took it to a mechanic. He tested the battery and told me that it was fine and it did not need to be replaced (OEM battery around 3 years old). The voltage was around 12V. I also did the diagnostic test that the car allows you to do and it also gave me a reading around 12.7V. I took the car back home and mistakenly turned on the AC for about 30 seconds while the car was in accessory mode...it instantly died. This time I went on Amazon and purchased one of those little jump starters and used it to jump start the car. Now it is running again but every day I dread that it will be dead again. Over the last 2 years I've had to jump it at least 5 times. Is there anything I can do to avoid this? I've read about car chargers, desulfination, trickle chargers etc and am very confused. I also don't know if I actively have to drive this car around or if I can simply turn it on in the garage and leave it on ready mode. Any advice appreciated.
     
    #1 Ozy, Jan 16, 2019
  2. dubit

    dubit Senior Member

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    Those short drives once a week probably just aren't long enough to keep a sufficient charge in the battery. I'd just pick up a battery tender at a Wal-Mart or auto part store. They're cheap. I use this one on my boat.

    BATTERY TENDER JUNIOR 12V - Walmart.com
     
    #2 dubit, Jan 16, 2019
    srellim234 likes this.
  3. M in KC

    M in KC Active Member

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    Also if you have the Smart Key option on your '05, disable it. The little black button under the steering column.
     
    #3 M in KC, Jan 16, 2019
  4. RobertK

    RobertK Member

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    Leaving the car in Ready mode is as good as driving it as far as battery charging goes. You should leave it on for several hours or even overnight if your intent is to charge the battery, since the car charges the 12V battery at about 2 amps. Turn everything else in the car off to minimize the time that the engine runs while you are charging the battery. If you are worried about security while the car is in Ready mode you can lock the door with the mechanical key.

    You can also reduce battery drain when the car is parked by turning off the SKS (if your car has it).

    A battery tender might be a better option for you if you have access to an electrical outlet where the car is parked.
     
    #4 RobertK, Jan 16, 2019
  5. Mendel Leisk

    Mendel Leisk Senior Member

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    I think you've answered your question, lol.

    Get a smart charger, 3~4 amp range, one that can be left on indefinitely, and use it. Put it on any day the car's not going to be used, then leave it on till it does see use.

    Your situation is very similar to ours. Me and the wife are retired, the car will sit 2~3 days, sometimes as much as a week. The next drive might just be to get groceries as often as not. I'm using a CTEK 4.3, leave it on pretty much around the clock.

    Hopefully you're secure parked, with 120 volt outlet available. Otherwise it get's problematic: you might need to look into battery disconnects, or solar chargers.
     
    #5 Mendel Leisk, Jan 16, 2019
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