Winter 12v strategy

Discussion in 'Gen 2 Prius Technical Discussion' started by James1964, Dec 5, 2018.

  1. James1964

    James1964 Member

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    12v is in good, working order but wondering if there is a strategy for keeping it that way throughout the winter cold?
    Thanks in advance for guidance.

    Posted via the PriusChat mobile app.
     
  2. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Do you drive it daily? Say 5~10 miles? Our sits, at least every other day, and to avoid background loads slowly eating away at the charge, I hook up a CTEK 4.3 smart charger on the idle days, just leave it hooked up untill next use. This is parked in an attached garage; would be a little more hassle in a driveway, not practical for street parking.
     
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  3. TomB985

    TomB985 Member

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    Just curious what you're looking to strategize, here. Most of us have been using lead-acid 12v batteries our entire adult lives to start cars...what exactly is different about this winter for you? Planning on storing the car?

    The Prius expects much less from the 12v battery than most cars, it just needs the power to switch on the hybrid system. I live in Minnesota, and I'm the 3rd owner of a Prius that's been here its entire life. 172K miles, and I just replaced the factory 12v battery two weeks ago.
     
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  4. sam spade 2

    sam spade 2 Senior Member

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    Cold weather is actually GOOD for the longevity of a battery......down to something like -30F or lower.

    WHILE it remains cold, there will be a slight temporary loss of capacity but that should not cause a problem.
    If it does, the battery needs to be replaced anyway.
     
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  5. TomB985

    TomB985 Member

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    Yep, that's exactly it...lower temps limit electrolyte evaporation. Batteries almost never survive 12 years down south, but mine was still showing 11.9v with the ignition on.
     
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  6. Mendel Leisk

    Mendel Leisk Sand Pounder

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    At start up it expects less, but while the car sits, like any modern car, it's imposing a low-but-constant demand on the battery.
     
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  7. bisco

    bisco cookie crumbler

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    instead of focusing on the cold, start paying regular attention to the batteries health, and consider a good maintainer like menders, if the car sits for more than a few days at a time, or your commute is only a mile or two.
    with a healthy battery, there is no concern, unless it will won't be driven for weeks at a time. but as it ages, a cold snap could damage it if it has been sitting, because there is a constant drain, so the voltage decreases each day.
    i don't think washington is as big a concern as other parts of the north though
     
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  8. James1964

    James1964 Member

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  9. sam spade 2

    sam spade 2 Senior Member

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    Well that's not exactly the reason. AGMs don't suffer from "electrolyte evaporation".

    A battery works by a chemical reaction. Because the chemicals are not pure the reaction is not perfect and some undesirable by-products are produced......even when it is just sitting there. That process slows down in the cold.
     
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  10. TomB985

    TomB985 Member

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    I did a bit of digging, and this is from the Optima battery website:



    Our Prius batteries are vented, would they not also be susceptible to water evaporation if other automotive AGM batteries are?
     
  11. Skibob

    Skibob Senior Member

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    Not quite. A vented AGM battery only uses the vent in an extreme situation. The general charging and discharging of the battery does not vent the battery.
     
  12. padroo

    padroo Senior Member

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    If the battery is healthy you will see your Prius start on mornings that leave cars with conventional starters stumble. Don't worry about it.
     
  13. sam spade 2

    sam spade 2 Senior Member

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    No they aren't.
    Having a vent tube for the pressure relief function is NOT the same as the cells being vented. They are NOT.
     
  14. rschlegel

    rschlegel Junior Member

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    I have a 2005 Prius with an original battery and live in Grand Rapids, Michigan. Approximately how many days can I leave the car idle before it will not start? I want to take a 2 week vacation via air!
     
  15. valde3

    valde3 Senior Member

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    It depends on the condition of that 12V battery. Nobody can tell without measuring it. If it’s really original it might not last many days.

    If the 12V battery is good and there’s nothing else wrong then couple of weeks is ok. If it’s a model with smart key system you should turn the system off by using the button under steering wheel if it’s parked for longer than a week.
     
    #15 valde3, Dec 10, 2018
    Last edited: Dec 10, 2018
  16. sam spade 2

    sam spade 2 Senior Member

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    Nobody can give a really good answer to that.
    If your battery really IS 13 years old, it could fail at any minute now.......in use or not.
     
  17. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Where will the car be for the duration of that flight, at the airport, at home but street parked, in a driveway, in a garage?

    If at all possible, I would connect it to a smart charger, one that can be left on indefinitely.

    That's what I'd say regardless of the battery's age. Still, I'm a little incredulous that you do indeed have a 15 year old battery: have you had the car since new?
     
  18. TomB985

    TomB985 Member

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    My car sat in the previous owners driveway for months before I test-drove and bought it, with the original 12-year-old battery. These cars really aren't much different in that respect than a conventional powertrain. There is a slow draw on the battery, and it reaches a point eventually where he lacks the charge to start the system.

    They're just not that picky, though. If your battery is factory like mine was, I'd be concerned regardless of time the car seats. But if it's newer and in good condition you will be fine.
     
  19. padroo

    padroo Senior Member

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    With the smart key system shut off you should be good for a couple of weeks. This is where the battery needs it's CCA checked to make sure it is up to snuff. I would drive it to a local parts store where they do battery testing for free and see just how good your battery is.
     
  20. Dustin Sletten

    Dustin Sletten New Member

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    I installed a cheap boat battery maintainer hard wired to 12v battery and the little charger unit self tapped to the plastic storage area. Simply plug it in on nights when it’s super cold or if I’m not going to use the car for a couple of days. Well worth it when after you price out the cost of a new 12v battery
     
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