12v Battery Issues

Discussion in 'Prius c Care, Maintenance and Troubleshooting' started by Plantz35, Dec 16, 2020.

  1. Plantz35

    Plantz35 New Member

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    Vehicle:
    2016 Prius c
    Model:
    Two
    I recently purchased a 2016 Prius C Two with 50k miles knowing it had the 12v battery replaced twice already.

    The battery died once while I was in the car with the accessories on and the engine off for 5-10 minutes but I was able to start it after about 5 minutes of trying.

    After putting 5,000 miles on it in the four months I’ve owned it, I got the oil changed. While in the bay at the oil change place, the car would not start. The accessories would turn on but the ready light would not. The technicians jumped the car and it worked.

    This morning it’s snowing and about 30 degrees outside. I tried to start the car and nothing happened. After trying for a few minutes, the accessories came on but not the ready light.

    I drive 120 miles in one trip two days out of the week and very sporadically the rest of the week, short distances of under 10 miles and some days not at all.

    The last time the battery has been replaced was some time last year. It seems like the battery needs to be replaced yet again, but it also seems like there is a larger issue causing the battery to die so frequently.

    TLDR, four year old car is on its third 12v and needs another. Can anyone help me from spending $150 on a replacement every year?
     
  2. bisco

    bisco cookie crumbler

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    welcome!

    if you are going to do this yourself, you'll need some tools.

    you have to get the spec for the quiescent draw when the car is off from the service manual.

    then with a digital meter, read the draw on your battery. if it is within spec, you just need a battery maintainer between drives.
    if it is outside spec, you have a major headache to track down.

    an alternative is to get a free load test at an auto parts store, and a recharge if the battery passes.

    then just keep a maintainer on it.
     
  3. jimnjo

    jimnjo Member

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    I can offer our experience, which suggests that all is not well with your C; a trip to Toyota or other specialist for diagnostics may be in order.

    We have a 2015 with around 33,000 miles, often left in the garage for 2 weeks or more without a trip and then not often more than 5-10 miles. We are on the original battery and have not had a problem starting at all. The garage is unheated and temps have been in the 20's and 30's the last few days (last time out yesterday). I expect to replace the battery next spring, unless we run into trouble this winter.

    The only thing I can think of that might run a battery down "routinely" is if the fob is kept too close to the car, and it continually 'recognizes' it. I don't know if this would be enough to run the 12v battery down (seems unlikely to me), and I would expect there to be fob battery issues as well if that is the case.

    It seems more likely something is "on" and draining the battery, though I only know enough to wonder just what kind of problem could cause that. Fault in the "on" switching? Or there are a few odds and ends on the dash and under the hood that come on from time to time, one of which might be 'stuck' on.
     
  4. PriusCamper

    PriusCamper Senior Member

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    Worked on my first Prius C last weekend... Was surprised at how much the 12v drained down with even something as simple as leaving the door open. But maybe as above commenter pointed out, the FOB was too close to the car? 12v voltage drains when car is off are fairly challenging. You're gonna need to become an expert on monitoring your 12v voltage and perhaps pull fuses to certain circuits when car sits to find the one that's draining. First step is to fully charge your 12v and disconnect it from everything in the car and confirm the voltage drain no longer is happening. Then hook it back up, but without the fuse for the interior lights plugged in. And just keep going through each system till you find it...
     
  5. sam spade 2

    sam spade 2 Senior Member

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    Given the reported history, I suggest that checking the charging voltage AND checking all the main battery cable connections also should be done before, or coincident with, the above.
     
  6. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Cool theory, and that would explain a lot of battery problems on many Priuseses, but not this one.

    The c trim One and Two have ordinary metal keys that the driver has to twist to make their cars READY. Trims Three and Four have electronic keys like the big Prius.

    This one will need traditional electrical troubleshooting: connect an ammeter at the battery, and monitor the readout as the car is closed, locked and 'abandoned.' And periodically afterwards too.

    If the draw is beyond the norm (I don't happen to know, but for many cars it is around 30ma) then it needs further investigation: pull fuses one at a time until the extra demand vanishes to learn which circuit is hosting the vampire.
     
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  7. Plantz35

    Plantz35 New Member

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    Thanks for the advice! With the battery under the back seat and the maintainer requiring an outlet (if I’m not mistaken) I may be able to rig this up but I dont think its the permanent solution I'm looking for.

    Thanks for the reply. The fob for my Prius is a physical key not an SKS. It has remote door lock features, if that could have an effect.

    I too am curious about something turning on without my knowledge but with nothing visibly happening its hard to know. The battery is acting like this is whats happening.

    I had my mechanic look at the battery and the connections and experienced the problem a week later.

    This is good advice, sounds like a pain but so is the car not starting. Thanks.
     
    #7 Plantz35, Dec 17, 2020
    Last edited by a moderator: Dec 17, 2020
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