12v Battery Is Discharging, Re-Charge Now !

Discussion in 'Prime Care, Maintenance and Troubleshooting' started by Rob43, Apr 18, 2020.

  1. Salamander_King

    Salamander_King Senior Member

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    I think where the diagram is showing for the jump stating procedure is the part shown in the photo by the red arrow. Doesn't any part of the bare metal frame would also work as a ground point? But I would not worry too much about where to connect the charger cable. For most of the external chargers, the manual explicitly states to connect the cable directly to the positive and negative post of the battery. In fact, if the battery is removed from the vehicle, that would be the only way to connect the charger. I don't think there is anything special about PRIME on this procedure.

    screenshot-priuschat.com-2020.06.10-15_25_25.png
     
  2. Halcykon

    Halcykon New Member

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    Yeah, honestly I always suspected the sks didn't shut off. Now I have proof.

    @Rob43 Yeah, I'm disappointed that my 12v would last 3 weeks tops. This is the 2nd, all new replacement too. I'm considering invoking the lemon law in my state (I'm still eligible), but I don't know if it's worth it...)
     
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  3. bisco

    bisco cookie crumbler

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    here, it has to go in for service 3 times, and keep failing. tough to prove with a quiescent drain. in fact, idk what toyotas response would be, but probably, 'that's normal'.
     
    #283 bisco, Jun 10, 2020
    Last edited: Jun 10, 2020
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  4. Hicksite

    Hicksite Member

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    Easier for me to use the ground strap bolt that is out in the open, not under the cover.
     
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  5. Rob43

    Rob43 Senior Member

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    Many cars have some type of annoying weakness, in the Prime it's this irritating parasitic 12v battery problem. So what I'm saying is this: Now that we know it exists there are many simple/cheap things that can be done to alleviate the problem.

    I personally charge up every once in awhile with my Battery Tender, plus I have my front mounted solar panel on 24/7.


    Rob43
     
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  6. bisco

    bisco cookie crumbler

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    nothing compared to gen 3 egr
     
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  7. RobertZ

    RobertZ Member

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    Okay so I landed on the right topic.
    With COVID-19 I have my Prime off-road (no insurance).
    Every few weeks it won't start.
    Luckily I have jumpstart thing that starts it up fine.
    First time I actually used another car.
    What's odd is that larger battery is fully charged.
    The hard part in this situation is that I can't charge the 12V battery using the car.
    What I mean is that it starts up in EV mode so engine does not come up.
    It won't let me switch to IC with the mode switch either.
    Just checking if I am doing anything wrong or other's have run into this...
     
  8. bisco

    bisco cookie crumbler

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    your post is a little fuzzy.

    it is not odd that the hybrid battery is full, but it is not good to just let it sit full.

    prime always starts in ev mode. not letting you switch to ic? (hv?) is prolematic
     
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  9. Salamander_King

    Salamander_King Senior Member

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    Few things to point here.
    First, you do not need to start the engine to charge the 12v battery. There is no alternator in prime. The DC-DC converter charges the 12v battery from the traction battery. If you have the traction battery charge left, then simply keeping the car in READY at PARK will change the 12v battery. If you run out of the traction battery charge, then ICE will start and charge the traction battery which in turn charges the 12v battery.

    Second, I don't know why you can not start the engine by switching to HV mode. Even with a full charge in the traction battery, switching out of EV mode and forcing HV mode will start the engine. Again, the starting engine is not needed to charge the 12v battery, but it should start as soon as you switch out of EV mode to HV mode.
     
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  10. Rob43

    Rob43 Senior Member

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    Please start charging your 12v battery ASAP with an external charger. If your 12v battery is still healthy (it's probably not) you can just put a simple trickle/maintenance charger on it and let it sit that way indefinitely.

    If your 12v battery is in trouble and needs a bigger push, put a ~6 to ~10 amp manual charger on it for a few hours to bring it up past ~12 volts. Then let your trickle charger finish the job.

    If none of this works, it's time for a new 12v battery...


    Rob43
     
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  11. RobertZ

    RobertZ Member

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    I do have trickle charger so I will try that.
    Other day I had to use my battery jumper power pack to turn the car on.
    After that it allowed me to switch gear and pull the car out of garage.
    I let it sit outside for 15-20 min in Park.
    I was able to put the car back in the garage later.
    I am sure battery is dead by now so I will connect the trickle charger.
     
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  12. RobertZ

    RobertZ Member

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    Update on my situation: I did trickle charge the battery for 5 hrs today and everything is seems normal.
    I can start the car, put it in reverse etc.
    I am going to let it charge over night.
    Reading other thread I had done two things that made matters worse.
    I had left car plugged in (no I didn't read the manual :)) for days and days.
    When I got it jump started, I should have left in Ready mode for a while (I didn't know it charges 12V battery in this mode).

    Lessons learned.
     
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  13. Salamander_King

    Salamander_King Senior Member

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    If you charge once a week or two, the battery will hold enough juice as long as your 12v battery is healthy. From my experience, you can also either drive once a week for 1-2 hours or just put the car in READY and PARK will keep the 12v charged enough, but over time the resting charge of the 12v battery does come down without an external charger.

    I just got this Onboard charger, I am going to install it on my PRIME this weekend. If I can also install an extension cord plug port, charging the 12v battery is going to be even easier.

    Screenshot 2020-06-12 at 7.06.03 PM.png
     
  14. PiPLosAngeles

    PiPLosAngeles Active Member

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    Is the solar panel not enough on its own? I was planning on grabbing one, but if it's not really effective I'll pass.
     
  15. Rob43

    Rob43 Senior Member

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    A 10 watt panel does not put out a lot of charge, but like anything there are many variables. Mostly your ability to feed it sunlight on a somewhat regular basis.


    Rob43
     
  16. PiPLosAngeles

    PiPLosAngeles Active Member

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    Mine's in the sun about 6 - 7 hours a day most days now that I don't drive to work much. Sometimes it sits for a few days and the battery gets pretty far below 12V.
     
  17. Rob43

    Rob43 Senior Member

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    It sounds like your 12v battery is in the same poor* (sulfated) condition that mine is in.

    It's easier for a simple 10 watt panel to keep a great condition battery fully charged under your stated conditions, I'd say it will have a tougher time when dealing with a poorer condition battery. Certainly you'd be giving it plenty of sun, so maybe your ~$20 dollar investment might workout. Many variables...


    Rob43

    * Sulfation typically takes place at or below 12.4 volts on a lead acid battery.
     
  18. Salamander_King

    Salamander_King Senior Member

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    I had to drive my wife for a dental appointment and wait for her in a car. 30 min drive to the dentist, ~3 hours wait at parking on READY mode, then 30min drive back home. Total ~4 hours charged up the 12v battery from 12.47v to 12.92v. While waiting PARK and READY, my traction battery SoC changed from ~70% to ~60% with audio on and A/C on and off intermittently.

    upload_2020-7-1_18-11-27.png
     
    #298 Salamander_King, Jul 1, 2020
    Last edited: Jul 1, 2020
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  19. Rob43

    Rob43 Senior Member

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    ^ That's a great result.

    But do you believe that Toyota Prime owners should be forced to figure this out for themselves and implement these procedures, or should Toyota have figured all of this out for the buying public ?



    Rob43
     
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  20. Salamander_King

    Salamander_King Senior Member

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    Yeah, PARK and READY for 3 hours is certainly much better than just driving for an hour. The question is, How short this PARK and READY can be to maintain the 12v battery topped up? 5 min was not sufficient. I have to try experimenting length of PARK and READY to sufficiently bring up the 12v battery from 50% (12.4v) up to 100% (12.9v). I also want to see how the 12v battery will be charged up during non-stop 3 hours drive.
     
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