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Did I leave the car on or door ajar?

Discussion in 'Gen II Prius Technical Discussion' started by rocketdoctor, Oct 13, 2009.

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  1. rocketdoctor

    rocketdoctor New Member

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    I tried to start my car today and the electric system was dead. When I jumped the car it started right up. At first I thought my wife had left the car running all night but I noticed their was still alot of gas in. Their was a door slightly ajar so maybe a light was left on?

    If a car is left on will it keep the battery charged enough until it runs out of fuel?

    Does the Prius know to shut off power ahead of time when the 12V gets low? soon as I jumped the car I was able to turn it off immediately and start it up without a jump. This is unlike other cars I had where you had to drive them around immediately or you would have to jump start it again.
  2. firepa63

    firepa63 Former Prius Owner

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    Most likely a door was left ajar and ran the small 12v battery down. The system will not prevent the 12v battery from depleting. If the car was in the READY mode the ICE would cycle to keep the traction battery charged. In turn, the 12v battery would be kept charged from the HV system. You should drive the car for at least 1/2 hour after jump starting to give the 12v battery a chance to recharge. Keep in mind that a deep discharge of the 12v battery will shorten its life.
  3. David Beale

    David Beale Senior Member

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    It doesn't take a lot of power from the 12V battery to "start" the Prius. Just a 50A pulse for 1/2 sec. will do it. So a battery you just "boosted" will probably restart the car.

    But that battery is nearly fully depleted, and will sulphate if left in that state. You should run the car for at least an hour to give it a reasonable charge. It actually takes about two to three hours in "ready" to charge it well. Note that with the Prius the engine doesn't actually have to be -running - to charge the battery. It's charged from the "traction battery" (the high voltage one) through a charger built into the inverter. The engine will cycle on and off as required to keep the traction battery charged. If the A/C system is on and calling for heat the engine will also run for that.

    As noted above, the 12V battery has now been "stressed" and will probably have a slightly shorter life due to that. Expect another two to three years life out of it if you don't fully discharge it again. Owners are averaging 3-5 years of 12V battery life.

    Beware of things like a door not fully closed, the interior light switches being left "on", and especially the hatch light, which is dim and very hard to see if left on with the cargo cover closed. Note that the interior light switches have two "on" positions. One keeps the light on even when all doors are shut.
  4. Eoin

    Eoin Active Member

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    If you lock the car every time you leave it it would be hard to leave a door ajar.
  5. Auntmimi

    Auntmimi New Member

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    14K miles on my 2006 Prius because it has set in a garage on and off two years while we were away, but always started right up when the battery was re-connected.
    I just drove it from PA to FL and after setting in the garage a few days, there is no power at all. I tried inserting the fob.....no go.

    Do you think it just needs charging or would it be safer to have it towed to a dealer? There is a possibility that the hatch was not closed entirely.

    Feel free to email me at auntmimi12@ymail.com. Thanks so much, The Villages, FL
  6. rocketdoctor

    rocketdoctor New Member

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    I know that but try telling that to my wife over and over again. in addition not locking the car makes it easy for someone to enter our house through the garage and its not uncommon for my wife to leave her Phone and wallet in the car.

    I read this interesting article on how much power is needed to jump Prius Startup Current so it makes a little more sense how my dead batter could start the car so easiliy after a jump.

    I had a long commute after jump starting so no problem recharging car.
  7. BAllanJ

    BAllanJ Active Member

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    With winter coming you should also be aware that a depleted 12v battery will freeze if it gets below 0 C and that will break the insides of the battery...ok, maybe that won't happen in lafayette... but we have a frost warning here for tonight.
    1 person likes this.
  8. kenoarto

    kenoarto Member

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    When is a door not a door? Whenn it's a jar!



  9. Patrick Wong

    Patrick Wong DIY Enthusiast

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    You could start by trying to charge the 12V battery. If that doesn't work, then replace the battery.
  10. richard schumacher

    richard schumacher shortbus driver

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    But be careful when jumping. As with many modern cars if you reverse the polarity it can do hundreds of dollars of damage. If you're not certain, have a dealer send someone to jump it, so that if they get it wrong there will be no question about warranty coverage.

    And get in the habit of always locking the car, no matter where you park or for how long. It will warn you of the most common battery-draining conditions.
  11. Auntmimi

    Auntmimi New Member

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    Thank you. We are 30 minutes from a Toyota dealer, should I trust AAA to jump it?
  12. David Beale

    David Beale Senior Member

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    Sure. Just make sure they don't use a 24V boost. They can access the 12V in the underhood fuse box. Plus 12V goes to a terminal under a red flip open cover. Negative to a bolt just above on the firewall. As soon as they connect you can put the car in "ready" and they can disconnect the boost cables.
  13. BAllanJ

    BAllanJ Active Member

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    I was wondering about the current requirements for a boost.... Do you think you could get what was required by hooking up a couple lantern batteries (6v) in series? 8 D cells? Just wondering in case of emergency.
  14. direstraits71

    direstraits71 Member

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    Here's the startup current waveform:

    Prius Startup Current

    The biggest consideration is the peak current which may go as high as 60 Amps that some times occurs depending on the status of the braking system when the start button is pressed.Overall the energy required is quite small.
  15. BAllanJ

    BAllanJ Active Member

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    Hmmm... not sure that D cells could do that.... maybe the lantern batteries... esp if the 12v in the car isn't completely dead yet. I actually travel with a booster battery in the winter... esp now that I can't boost others w my car. Some of us Canadians feel it's quite antisocial not to provide a boost to someone in need... winter can kill.
  16. David Beale

    David Beale Senior Member

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    A NiCd or NiMH "D" cell battery could do it if it is built with good connections, but a ZnC battery, no.

    A smallish gel cell 12V battery will also work. If you intend to carry one the best is the emergency boost packages that plug into the cig. lighter so they charge when the car is in "ready". That guarantees it will be fully charged when you need it. You will still need to connect it to the "boost terminal" under the hood or the battery under the floor in the right side of the hatch. I doubt the cig. lighter plug could supply the current pulse needed, even if it was connected, which it is not.
  17. adamace1

    adamace1 Senior Member

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    I wonder if yu hooked a 12v battery into the cig lighter and gave it like 5 mins would the car start?

    I amalso coming to the conclusion that i should get a booster and keep it in my car incase i have a dead bettery. But even better i can use it to help others who need a jump
  18. greenthumb25

    greenthumb25 New Member

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    I think they should put that feature on the new models. it's just a good idea because people forget these things all the time
  19. David Beale

    David Beale Senior Member

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    No. As I said (well, intimated) in my last post above, the cig. lighter and accessory plugs are disconnected when the car is off. If your 12V battery won't put the car in "ready" then they stay disconnected. It's -possible- there might be enough power in the "dead" 12V battery to get to accessory, in which case you -could- charge the 12V battery from the cig. lighter plug, but it would take a long time, as there wouldn't be a very big voltage difference to drive the current and there -would- be a fairly high resistance from the cig. lighter plug to the battery (perhaps 0.5 ohm or so minimum).

    Best to use the jump point in the underhood fuse box. It's easy to access, easy to find, and will work! If you want to build your own cables for "boosting" a Prius you can use the mid-size clips you find on most electronic "clip leads". I recommend #10 wire though, and not more than about 8' of it.
  20. DetPrius

    DetPrius Active Member

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    I believe GM cars now shut off interior lights after a certain period of inactivity, regardless of all switch positions. This would save a lot of jump starts and shortened battery life. This should really be on all cars, especially if you have kids who like to have interior lights on while on the way home so they can read books. :)
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