Accessories running down battery when car stopped

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by RachelP, Feb 6, 2020.

  1. RachelP

    RachelP New Member

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    Hi there!

    I have a 2010 Prius from Japan, have only had it a few months, and have had no issues at all with it until today

    Today I used a new 12V, 2.4A fan in my prius (for my dog in the trunk) plugged into the power socket between the front seats

    First time around I ran it with the Prius in accessory mode (one push of the power button), for half an hour. This completely depleted my battery so that the car wouldn't start. Fair enough, I figured it was just too much draw for too long on the battery.

    I got a jump start, went for a 20km drive, then left the car turned on but in park for half an hour with the fan running. Again, the battery depleted and the car wouldn't start. During the period we were parked the dash battery showed 3 bars, when it dropped to 2, the engine kicked in for 5 minutes.

    Help - this makes no sense to me. Can anyone shed some light?

    Thanks
    Rachel
     
  2. JC91006

    JC91006 Senior Member

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    You need to fully charge the 12v battery and test it (with a car battery charger for about 10 hours). If it fails a load test, you'll need to buy a new one.

    You also should not run anything on accessory mode for more than 15 minutes, the little Prius battery will drain easily and leave you stranded again.
     
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  3. Pluggo

    Pluggo Active Member

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    12v car batteries are not expected to last 10 years, even in a Prius. If you are using the original, change it now.
     
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  4. frodoz737

    frodoz737 Top Wrench

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    After the jump, you drove 20 km and then left the car in P with the car still in ready mode...and it wouldn't start (next time?) A healthy battery takes little juice to boot the car and that cycle given after should have been more than enough. Check you cables for corrosion, but sounds like you just need a new 12 VDC battery.
     
    #4 frodoz737, Feb 7, 2020
    Last edited: Feb 7, 2020
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  5. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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  6. fuzzy1

    fuzzy1 Senior Member

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    Do note that the Prius' 12V charging system is surprisingly slow. It takes many operating hours to bring a flat 12V battery up to a reasonable charge. 20km is only 10-20 minutes, so your 12V battery was still almost flat. An overnight charge from a plug-in charger or battery tender would do far better.

    Though this doesn't explain why a car left in "READY" mode, quit running.
     
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  7. jerrymildred

    jerrymildred Senior Member

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    You figured correctly. As already mentioned, keep it in READY mode to run accessories. The battery is sized to boot the computers and close some relays, not to run fans and stereos.

    This is exactly how it should work. The indicator on your dash, if you weren't already aware, is for the traction battery, not the 12V battery.

    Yeah, a short drive is not enough to recharge a dead 12V in pretty much any car. If it would need several hours connected to a dedicated battery charger, there's no reason to expect it to be faster with the car's charging system.
     
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  8. ASRDogman

    ASRDogman Senior Member

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    I run a fan I put on my dogs crate in the back. I changed the 12v supply in the center console to
    supply power all the time. I run it about 30 minutes, off for 30 minutes, then run it for about 45 minutes.
    My Prius starts each time. The battery is almost 2 years old.
     
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  9. RachelP

    RachelP New Member

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    Thanks everyone!

    I've had the battery tested at a shop and they say it's a pass. It's definitely not the original one, there's a label on it saying it was installed in Sept last year.

    It's been starting fine since the incident last week & I've used it almost every day since then, so I'm going to give it another go running the fan when it's in stationary but in "ready" mode to see if it copes for an hour or two, and if not, I guess I'll try a new battery even though this one is supposed to be good?

    ASRDogman - nice malli! What sport do you do? :)
     
  10. ASRDogman

    ASRDogman Senior Member

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    You probably need to charge it from time to time since you don't drive for long periods.
    I drive 2-3 hours at a time 4-6 times a week, so it get a good charge.

    No sport, ASR, American Street Ring.


     
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  11. RachelP

    RachelP New Member

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    Thanks. I just left it in ready with the fan running for 45 min and it was fine afterwards, so perhaps last time the battery was just uncharged because I'd previously drained it.

    Cool - we don't have that here, I'd never heard of it before, but your username makes a lot more sense now!
     
  12. jerrymildred

    jerrymildred Senior Member

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    Keeping it in READY will let it run the fans till you run out of gas in a few weeks, assuming a full tank. As long as it's in READY, the DC/DC converter will feed power from the traction battery to the 12V battery to maintain that level. Makes no difference if the engine is running -- just so it's in READY mode. The engine will run whenever it needs to add charge to the traction battery. People camp overnight in the Prius all the time this way.
     
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  13. wheezyglider

    wheezyglider Active Member

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    What about running a fan off of one of those USB power banks -- the kind mostly used for charging cell phones? The power bank only charges when the car is on (READY or ACC). When the car is off the fan can only ever deplete the power bank and not the 12V battery.
     
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  14. ASRDogman

    ASRDogman Senior Member

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    Or a UPS backup battery. They are about $15-20 depending on size you get.
    Then you can have it hooked up the the accessory plug that will charge up that battery only when
    the car is on. (y)

    Update: I found this link: Mighty Max 12v 7000 mAh Compatible Battery for UPS APC Back-UPS BX1000 - 2 Pack 730052395754 | eBay

     
    #14 ASRDogman, Feb 16, 2020
    Last edited: Feb 16, 2020
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  15. jerrymildred

    jerrymildred Senior Member

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    Ooooh. Don't mislead like that. The car only charges the battery in READY mode. That's the only mode where it charges the battery. Check the manual if you're not sure.
     
  16. jerrymildred

    jerrymildred Senior Member

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    Rats. Too late to edit my previous comment. I should have added:
    But don't feel too bad. I've made similar mistakes as have most of us. It's just that that mistake can leave you stranded. Hence my alarmed reaction.
     
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  17. Grit

    Grit Senior Member

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    How will you control the current going from car to battery? These apc battery will blow up if the recharging current is beyond spec charge amperes. I replace these in the it field on a regular basis, I wouldn’t throw a 12v source to it without amperage control.
     
  18. Grit

    Grit Senior Member

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    On acc, power still sends to power bank if connected to 12v cigaret plug. But if you leave it plugged in with car off, you run into the issue of car keep unlocking when you try to lock the car
     
  19. ASRDogman

    ASRDogman Senior Member

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    Considering that the person will have the fan blowing for a while, the battery will be low.
    He stated he doesn't drive that much so it's doubtful that battery would get fully charged at
    1-2 amps.
    It was just an option, to consider.

    Results may vary.

     
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  20. wheezyglider

    wheezyglider Active Member

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    Uh Jer, this is the kind of power bank I'm talking about. You charge it when you're driving or when parked in ACC mode, then use it when the car is OFF. You'd have to reallllly work at it to strand yourself this way. (Fun fact: In Gen 3 lift-back ACC mode turns off after 1 hour. In PiP it's only 15min.)
     
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