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

Preventing dead battery after 6 weeks

Discussion in 'Gen 4 Prius Main Forum' started by priuswarrior1989, Jun 19, 2021.

  1. priuswarrior1989

    priuswarrior1989 New Member

    Joined:
    Jun 19, 2021
    2
    1
    0
    Location:
    California
    Vehicle:
    2017 Prius
    Model:
    LE
    Hello Friends,

    About a year ago, at the beginning of Covid, I went around 6 weeks without driving the car. When I tried to drive it, the 12v was dead. Since then, it never held a charge, despite driving it + letting it charge. I replaced it with another 12v.

    I'm likely not going to drive it again for ~6 weeks. I was thinking of disconnecting the battery to prevent the same issue.

    Two questions for the group here:
    1. Is disconnecting the battery the best option or is there something else I should be doing? (I'd rather not keep a trickle charger plugged in.)
    2. How + What do I disconnect? Ex: Do I disconnect the negative or positive? Do I have to use special pliers when dealing with live wires?

    Thank you!
     
  2. jdenenberg

    jdenenberg EE Professor

    Joined:
    Nov 21, 2005
    3,837
    1,828
    1
    Location:
    Trumbull, CT
    Vehicle:
    2020 Prius
    Model:
    LE AWD-e
    When dealing with car batteries always disconnect the negative first (and connect it last) so that accidentally touching any metal part of the car with the wrench will not cause a short circuit (and sparks). You can easily disconnect the negative cable where it connects to the car body.

    JeffD
     
    Valiant V and FuelMiser like this.
  3. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,751
    48,963
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    just disconnect the neg and you'll be fine. you might have to reset a couple things on power up, but nothing important.
    the only other option is the trickle charger (maintainer)
     
    Valiant V and Mendel Leisk like this.
  4. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

    Joined:
    May 12, 2018
    6,826
    6,473
    1
    Location:
    Pennsylvania
    Vehicle:
    2018 Prius c
    Model:
    Two
    You can buy a disconnect switch to install between the negative battery terminal and its associated wire. They only take a few minutes to install, and they're extremely simple/robust/reliable devices. It would make the periodic disconnect/reconnect a very quick, safe, no-tools experience.

    Screen Shot 2021-06-20 at 6.07.54 PM.png
    (generic example pictured)
     
    Valiant V likes this.
  5. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,302
    15,094
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    In many Prii there is already an easy way to disconnect the battery. Gen 1 and Gen 2 had a fat cable going to the battery positive terminal clamp with a plug-in connector you could just squeeze and unplug, in a plastic housing that you don't have to worry about sparking to nearby metal. Gen 3 did not have that, but has a big fat white wire right in the underhood fuse box that can be unplugged the same way, to the same effect.

    I haven't looked that closely at a 2017, but I wouldn't be surprised if there's a similar way.
     
  6. FuelMiser

    FuelMiser Senior Member

    Joined:
    Jun 29, 2008
    1,268
    860
    0
    Location:
    Monument, CO
    Vehicle:
    2016 Prius
    Model:
    Touring
    Yes, and then you can wrap a towel around the disconnected negative cable to further isolate it from under hood components. Also, if your goal is just to leave the battery offline, just leave the negative cable wrapped up under the hood. You'll probably have to lock the car with the metal key because door locks will be inoperative. Make sure the trunk and the other door locks are secured manually and then lock the driver's door with the key. When you get back, you can unlock the driver's door with the metal key and release the hood. Reconnect the negative battery terminal and you should be good to go.
     
    Valiant V likes this.
  7. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    23,302
    15,094
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    I haven't seen enough photos of the 2017, but if it's got an unpluggable main cable somewhere like Gen 1, Gen 2, and Gen 3, then you don't even need to wrap a towel around anything.
     
  8. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,694
    38,234
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    @priuswarrior1989 what's your parking situation? If you've got secure parking and AC current outlet, consider getting a smart charger, one that can be left on indefinitely, if need be. That's our scenario: sporadic use, secure parking and AC outlets available. I use a CTEK 4.3 charger, and I've installed it's quick connect under the hood, for convenient connection.

    If you don't have secure parking, I'd second the disconnect/isolate of the neg battery connection.
     
    Valiant V and fotomoto like this.
  9. fotomoto

    fotomoto Senior Member

    Joined:
    Apr 22, 2009
    5,597
    3,771
    0
    Location:
    So. Texas
    Vehicle:
    Other Hybrid
    In the just-in-case department, park the vehicle so the hood is easy to get to and (worst case) be towed out. I would also suggest fully charging the 12v before disconnecting it.

    Long term storage: also see rodent/pest issues.


    GOOD LUCK!
     
    Valiant V likes this.
  10. priuswarrior1989

    priuswarrior1989 New Member

    Joined:
    Jun 19, 2021
    2
    1
    0
    Location:
    California
    Vehicle:
    2017 Prius
    Model:
    LE
    Thank you! Do I just leave the cable hanging or should I wrap it with electrical tape or something?

    Thank you! Is the towel a fire hazard? Additionally, is my goal to avoid the cable from touching the battery terminal or any other metal portion of the car?

    Thank you! Ahh, unfortunately I don't have an outlet nearby.
     
    Mendel Leisk likes this.
  11. systemr

    systemr Junior Member

    Joined:
    Feb 20, 2017
    7
    5
    0
    Location:
    SF
    Vehicle:
    2018 Prius
    Model:
    Two
    second the battery tender, but can't a prius go longer than 6 weeks w/o being driven? I'm pretty sure I've left mine undriven for that period of that time in the past...
     
  12. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,751
    48,963
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    depends on the prius, and the health of the 12 volt
     
  13. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,751
    48,963
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    you can just leave it hanging. the negative does nothing, unless it touches the positive :eek:
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,694
    38,234
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    The neg cable is typically disconnected at the post, and it's other end left connected to bare metal on the body. One issue is that the cable is pretty short, and having spent years connected to the post, has "memory", may want to relax back towards that post. If it touches it's not a short, but it will be connected intermittently, and may spark a bit. Bottom line, it doesn't hurt to take measures to isolate it.

    My typical scenario for disconnecting it is during brake work; what I do is stuff the loose cable end into a leather glove, and the other glove I lay over the latch mechanism on the hatch threshold, so the the hatch can't lock on me.
     
  15. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,751
    48,963
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    this being a 2017, i'd be curious to see a disconnected negative cable under the hood. on my dakota, it just falls down below the battery
     
    Mendel Leisk likes this.
  16. Mendel Leisk

    Mendel Leisk Senior Member

    Joined:
    Oct 17, 2010
    54,694
    38,234
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    Yeah know your audience… :oops: