1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Is it normal to have a dead 12V after 2 weeks of non-use?

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by Halcykon, Apr 21, 2020.

  1. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    I've been talking to the Toyota Customer Experience Center and my local dealership and they found nothing wrong with my car.

    They only thing they recommend is to drive my car 1-2x a week to prevent my 12V from dying.

    I'm a little skeptical since this is not mentioned in the owner's manual at all (P.80 talks about driving the car once every few months to charge the hybrid battery). I've also been seeing accounts of other Prius cars lasting a month in between drives. Is this possibly a Gen 4 issue?
     
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    yes, gen4 electronics seem to be putting a higher drain on the battery than previous gen's,

    that being said, if it is the original battery, there have been a large number of defects
     
  3. alanclarkeau

    alanclarkeau Senior Member

    Joined:
    Feb 24, 2016
    7,041
    7,580
    0
    Location:
    near Brisbane, Australia
    Vehicle:
    2016 Prius
    Model:
    N/A
    There have been a couple of similar threads recently - maybe check them out.

    "...large number"? - I think it's just a few really. Most are fine. Mine is almost at 4 years old, and have had no problems.
     
  4. Salamander_King

    Salamander_King Senior Member

    Joined:
    Nov 8, 2015
    10,958
    8,836
    0
    Location:
    New England
    Vehicle:
    Other Hybrid
    Model:
    N/A
    Follow this thread. I am checking the 12v battery on PRIME (same 12v as Ge4) for a week without driving. I have never let my car sit longer than a few days before. But with the current lock-in situation, I am driving the car only once a week. I am still on 2nd day, but interpolating the data so far a fully charged battery 100% at 13.06v will have 50% or 12.01V in 1 week. So, yeah in 2 weeks, it can be low enough not to be able to start the car.

    12v Battery Is Discharging, Re-Charge Now ! | Page 2 | PriusChat
     
  5. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    right. when i say large number, i mean relative to past complaints. we've had a bunch here, not seen in past generations. still unknown whether it is the batteries or defective systems.
     
  6. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    7,035
    2,780
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    (EDIT) Wait a sec. I was just reminded in another thread that the Gen 4 vehicles use a conventional wet cell battery mounted in the engine bay. If that is correct......have you checked the "water" level in the battery lately ? That is critical for proper battery operation and health.

    (original response)
    NO. It's mostly a life style issue.
    IF....your normal usage included a lot of short trips OR a lot of down time, then your 12 V battery likely was "low" when you parked it and that is hard on them.
    If you have access to AC power where it is parked, a small battery tender is HIGHLY recommended.
    If not, a half hour drive every 2 weeks should be enough to keep it going........IF it is fully charged to begin with.
     
    #6 sam spade 2, Apr 22, 2020
    Last edited: Apr 22, 2020
    MarkMassachusetts likes this.
  7. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    What's weird is that the dealership tested my prius for parasitic draw and it came back at .03 amps (officially said .03 milliamps but I think that's a typo)
     
    bisco likes this.
  8. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    Interesting about the water level. Is this the same thing as battery fluid? The battery is 6 months old so I'd be surprised, but I'll ask the dealership today.
     
  9. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    7,035
    2,780
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    Yes. Same thing.
    Just because the CAR is 6 months old really says nothing about the age of the battery.
    They can be 6 months to a year OLDER than the manufacture date of the car......which can be up to a year before it is sold.
    And sitting around unused is WAY harder on wet cell batteries than the previous AGMs.

    AND.....even perfectly healthy and fully charged, conventional wet cell batteries "self discharge" at a rate 5 to 10X as fast as an AGM.
    Toyota did NOT go back to the old style batteries because they are in any way better..........except for the cost.
     
  10. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    Update:

    I took it to another dealership for a second opinion (long story, but there's a mechanic I like and he diagnosed the first 12V failure when another mechanic said there wasn't one).

    Long story short, he diagnosed a battery failure in this 12V as well (after another mechanic said there wasn't one). I got it replaced, so I'm on to my 3rd 12V after 18 months of owning this Prius! I'm thinking of leaving this one un-used for 2 weeks just to see if it's really the 12Vs or a defect with my car.
     
    #10 Halcykon, Apr 22, 2020
    Last edited: Apr 22, 2020
    Rob43 and bisco like this.
  11. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    My car isn't 6 months old, but your point still stands. That makes sense
     
  12. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    there's a thread by @Rob43 regarding prime 12volts. it might be worth your perusal
     
    Halcykon likes this.
  13. Rob43

    Rob43 Senior Member

    Joined:
    Sep 24, 2014
    1,373
    1,044
    0
    Location:
    VA, BMW Race Car, BMW R1200R, BMW 330Ci, Ford F350
    Vehicle:
    2013 Prius v wagon
    Model:
    Prime Advanced
    As others have mentioned, I've got a thread on this you should look into. Hopefully you leave your new battery alone as it should be charged and in great condition, then just monitor it daily for the 2 weeks that you mentioned. Try to follow the outlined testing procedure below and log your results, then please post up any findings of your lower voltage in my linked thread.

    12v Battery Is Discharging, Re-Charge Now ! | PriusChat

    Testing Procedure:

    For those of you that would like to add your own testing results to this thread, here's what you need to do:

    1) Fully charge your 12v battery using some type of external 12v battery charger.
    2) Leave your car locked, BUT unlatch your hood so that you can access your 12v battery later without waking up the Primes computer. (Keep your key fob away)
    3) Once each day after your initial full charge, check and measure your 12v battery voltage with a voltmeter and log your results.
    4) Assuming you have other cars to drive, test for as many days as you conveniently can, the longer the better. For battery safety reasons, terminate your testing at roughly ~11.9 volts which is about ~40% for a 12v battery.
    5) Re-Charge your 12v battery with your external 12v battery charger and bring it back up to a full charge.
    6) Your testing is done, please post up your daily logged testing info.


    Rob43
     
    Halcykon likes this.
  14. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    Could I safely assume that a Prime gen 4 operates pretty much like a Prius 2?
     
  15. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    Thanks Rob! I'll try this.
     
  16. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    7,035
    2,780
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    The trim level number that follows the Prius name has NOTHING to do with the design generation number.....which isn't obvious to a casual observer. :)
     
  17. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i suspect so, but a couple things come to mind: prime charges the 12v along with the hybrid battery when plugged in, albeit a very small amount.
    due to the electronics, prime may have more quiescent draw, but that's only a thought, don't know anything for sure.
     
  18. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,474
    38,106
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    jerrymildred likes this.
  19. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    yup, you gotta navigate carefully
     
    Mendel Leisk likes this.
  20. Halcykon

    Halcykon Junior Member

    Joined:
    Apr 12, 2020
    28
    13
    0
    Location:
    Sugarland
    Vehicle:
    2018 Prius
    Model:
    Two
    Hi @Mendel Leisk , yes these are both me.

    I posted the first one when I was feeling very frustrated with my car and it was more of a "I don't know what to do next with this problem".

    I posted this one after some thought and wondering if this is actually normal behavior. Sorry if I'm breaking priuschat rules, I'll delete one of the threads if this looks like I'm spamming.

    @bisco, I'm not sure what you mean.