Bad 12V battery -- with advance warning!

Discussion in 'Gen 3 Prius Technical Discussion' started by justphilly, Jan 11, 2021.

  1. justphilly

    justphilly Junior Member

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    As far as I know my 12V battery is ten years old. I have never replaced the battery, and the car is a 2011 model that I acquired in 2017. Needless to say it is reasonable to guess that the 12V battery may be reaching its end of life.

    Until recently I would put the car in "IG-ON mode" (what you get when you press "power" twice without touching the brake pedal, to turn the car on)... and in this mode I'd use a 12V tire inflator to pump tires up to the desired level. Sometimes doing this many times a week, because at the time I had slow leaks in one or more tires.

    Anyway, doing this does NOT connect the HV battery so it's the 12V battery that is operating the tire pump as well as anything else (radio, lights) that may be on at the same time. There will be plenty of charge in the HV battery but the voltage runs low on the 12V system because the HV battery isn't running.
    Anyway this gave me warning that my 12V battery is starting to go. The speed of the compressor started to get really slow (you can hear the pitch and loudness of the thing decline like it's struggling to do any work).

    Well, today I couldn't get the car to "start" while the brake vacuum pump was running. Had to wait until it stopped running (it was going slooooow) and give the battery a little rest and THEN I could start the car.
    I ordered a 12V battery replacement. I'm hoping the car continues to start every day til the battery arrives. In the mean time I'll see if I can remember to avoid triggering the brake vacuum pump before I have the car fully switched on (HV battery connected) and be sure to switch the lights fully off before shutting down.
     
  2. ChapmanF

    ChapmanF Senior Member

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    Once you get your new battery, try your air pump routine with the car just in ACC (one push, no brake pedal) instead of ON (two pushes, no brake pedal). I think the power outlets are active in ACC, but a lot of the car's normal electrical loads are not; that way you're not sucking as hard on the battery while there's no support from the hybrid system.

    I had one of those little inflators once, but I eventually wired a larger compressor into the car instead. That solved a few things that used to annoy me:

    • There's no TPMS in the spare, and I'm really bad at remembering to regularly check it. When I wired in the compressor I just set it up to keep the spare at 60 psi, out of sight, out of mind.
    • Instead of a little slow inflator to plug in and lug around, I just have a coiled-up air hose living in the small storage bin off to the left of the hatch area. It's always connected to the spare tire, which is always 60 psi. That'll top off any of the four lower-pressure tires in seconds, just push the chuck on and squeeze the trigger, much faster than the typical small inflator.

    With a blow gun on the end it's also great for blowing tree gunk out of gaps and under the hood, etc., and a few times I've used other small air tools (but only for very light work).

    [​IMG]
     
  3. abubin

    abubin Member

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    How about you check the voltage of the battery? It is also good indication of the battery health.

    Also, you can now get those battery operated tyre pumps. I am using Xiaomi portable air pump and it works great. I too have small leaks on two of my tyres.

     
    #3 abubin, Jan 12, 2021
    Last edited: Jan 12, 2021
  4. ASRDogman

    ASRDogman Senior Member

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    If you have small leaks, you should find out why. You either have a nail, or screw, or some other object
    in the tire causing the leak. Or the valve is not completely sealing, or the valve core is leaking.
    Or the tire is not sealing around the rim.....
     
  5. sam spade 2

    sam spade 2 Senior Member

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    An even better plan is to actually put the car into "ready" mode to put some power back into the 12 V battery and don't obsess if the gas engine actually starts for a minute or two.
    Yes, at this point I agree that a new battery is probably needed. Along with a way to fully charge it.

    An even BETTER plan is to get your tires fixed.
    WalMart does it for about $7.50 per patch-plug device......assuming it is a simple puncture.

    What ever is causing it may suddenly fail completely while going down the road.
     
  6. abubin

    abubin Member

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    I found my tyre leak. It's from the valve stem. Only way to fix it is changing the valve stem. I might as well change the tyre cause it's due anyway. Just waiting for some good deal on the tyres as mine is using 18" low profile tyres which cost a lot for 4 pcs of good quality low noise brand.
     
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    It’s a so-so indicator? An electronic load tester is better. I’d recommend Solar BA9.
     
  8. ASRDogman

    ASRDogman Senior Member

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    That's good! You can use any valbe core. Even from a bicycle tube.
    That would keep you from having to constantly fill the tire.
    Or is it the actually vavle where it's attached to the rim?
    There's a kit to repair the TPMS unit. Or when they replace the tire they can remove it,
    clean around where it attaches, and reinstall it. MAYBE a dab of silicone to seal it.

     
  9. ChapmanF

    ChapmanF Senior Member

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    Toyota sells the washer and the nut separately that hold the TPMS sensor/stem in place; they can be replaced from the outside, are not considered reusable, and should be replaced with new any time they're removed.

    There's also a fitting kit that includes both of those and the grommet that goes on the inside. The tire has to be dismounted to do that.

    Yire shops should have versions of those parts in stock, because they're officially supposed to loosen the sensor/stem before any dismounting of a tire, and reattach it with new grommet/washer when remounting.
     
  10. justphilly

    justphilly Junior Member

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    An update - my new 12V battery arrived about 24 hours after I ordered it (a couple days before I thought it'd arrive) and it works fine. Decided not to experiment with LiFePO4 this time 'round even though I'm familiar with such batteries having used them for E-bikes.
    Oh, and I do my own tire repairs. Walmart is far from home AND in my area takes an hour to do anything at all on customers' cars.
     
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