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12 volt battery drain after 3 weeks non use- normal?

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by priusrust, Mar 13, 2023.

  1. priusrust

    priusrust Member

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    Hello,
    After 3 weeks or so of non use, 12 volt battery does not have enough juice to start car....use cables to another battery start it. It is a relatively new battery ..is this normal.??
    How long can your car sit without using before 12 volt is drained? Thanks in advance!
     
  2. sam spade 2

    sam spade 2 Senior Member

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    Define "relatively new".

    And how often does it sit for more than a couple of days ?

    Yes, reports similar to that are very common.
     
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  3. FuelMiser

    FuelMiser Senior Member

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    Are you talking about a Gen 4 (2016+) or the 2004 Prius from your signature? The new Gen 4 use a different 12V battery than earlier gens. 3 weeks on a "relatively new" battery should not deplete it. You can take it to an auto parts or battery store to have it load tested.
     
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  4. ColoradoBoo

    ColoradoBoo Senior Member

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    I think it's normal...there's numerous things that draw from the 12-volt when it's parked. (The wireless keyfob system, the evap emission system) even opening the driver's door will make the brake actuator pump up the system...that's the noise we hear.
    If you're able, putting a 'battery tender" on it when you park might not be a bad idea. If you can't, making sure to drive her for 15-20 miles a week isn't a bad idea. (With few electrical things on so the 12-volt battery gets all the extra juice.)
    I, often, check our 12-volt batteries and if they haven't been driven in the past week or so it will suggest charging the 12-volt...I've never had a car do this....one of the many quirks of a hybrid!
     
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  5. bisco

    bisco cookie crumbler

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    Agreed. Without knowing the age and state of charge when you parked it, it could be normal. Or not
     
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  6. priusrust

    priusrust Member

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    Thanks for all this input- much appreciated! Yes, this is a 2016, not my 2004. Some background: this car may suffer from too little driving. I got it from my dad, who occasionally drove it. He had the same problem, dead 12 volt. My guess at that time was that he put the car in park, and after pressing park button, assumed he had pressed on/off button... and left car on. (easy to do!) But I really did not know. Since his battery was 5 years old, he decided to have the dealer put in a new one just in case. So.....the current one is about 2 years old . To be clear, this car spends life being parked much of the time. 24k miles on a 2016 tells the story. So.....on a 2 year old battery, 3 weeks idle draining it seems a bit questionable (?) So, wondering if I forgot to 'turn car off' (assuming that would be a cause). I'll look into a 'battery tender' thanks! ...............For the record, I miss the gen 2. Perfect amount of tech imo. Currently, lots of little bells whistles that are supposed to add convenience adding 5 inches to the owners manual. ::end rant::
     
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  7. Doug McC

    Doug McC Active Member

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    Try reading the Gen 4 Owners Manual and it will explain that “3 weeks OR SO” might just lead to this problem (ESPECIALLY when it is a common occurrence (the “3 weeks or so)). Let any modern vehicle with the anti theft devices sit and it eventually leads to dead batteries. It is NOT a Prius “problem”. Owners can prevent some of these issues by learning how to reduce the drain on the battery (again, explained in that little used resource referenced.
     
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  8. Mendel Leisk

    Mendel Leisk Senior Member

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    Are you parked in a garage, or at least close to 120 volt outlet? If so consider getting a smart charger.

    our 2010 has only around 65k miles, usage diminishing a lot of late: it more or less lives on a charger.
     
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  9. FuelMiser

    FuelMiser Senior Member

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    For the record, leaving the car in Park without pressing Power will continue to charge the 12V battery! The 12V is charged from the Traction Battery when the car is in READY and not in Neutral. Furthermore, the gas engine will switch on to recharge the traction battery as needed while in this state. The only real threat to running down the 12V is using Accessory power by pushing the Power button without the brake pedal pressed. Thus, the car is not in READY and only powered by the 12V.
     
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  10. Doug McC

    Doug McC Active Member

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    While leaving it in park will allow the 12 volt to be charged, it will shut down after ~30 minutes (at least in the’22’s, also explained in the seldom used document). It would be an interesting experiment to see if there is a difference in the parasitic draw between a proper shutdown versus an auto shutdown.
     
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  11. priusrust

    priusrust Member

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    Doug McC : re seldom read document (aka 'war & peace')....good point. Just not have had a chance to peruse. Pages on end of frivolous bells and whistles minutia repels...
    Fuelmiser: re leaving it in park-power on. I knew this applied to my 2004....just spaced it out. I have an inverter hooked up to 12 volt in 2004....can cook, etc while parked. Toyota should build these into prius. Fascinating feature. I think I could have cooked a roast beef dinner in an instapot hooked up to inverter while driving (?).....park for night leave car 'on' to maintain constant temp if needed. If DougMcC is right and it shuts down after 30 minutes...then this would not longer work.
    Mendel: gonna get a "battery tender jr' -thanks for tip!
    Why I miss my 2004:- Despite its faults (wheel bearings, brake actuator, steering -!! mine disconnected while driving! sued toyota , but lost), oh, little leak high on back hatch that rots out battery well, and corresponding area on right side- my battery was dangling over road held on by cables!!) 2004 is a tank! just right amoutn of tech. (no 2016, I dont need cutesy video of car driving everytime I start up!) , glove box-2016 useless...way down low hard to access. 2004 perfect. 2016 Headlights: modern harsh white blue lights impossible to change bulb. Sure, save some deer, but blind oncoming drivers. end rant.
    DougMcC : like your Einstein quote. This one has been on my mind lately:

    "A world federal government with powers adequate to guarantee security is not a remote ideal for the distant future. It is an urgent necessity if our civilization is to survive."
    "Only by transferring military power to a supranational body, which derives its moral and legal authority from the fact that it genuinely represents individual member nations, will peace be secured. Peace cannot be achieved by gradual development, peace requires a decisive radical step..." ~ Albert Einstein

    Thanks for all this advice!
     
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