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How to jumper or charge 12 V battery

Discussion in 'Gen 3 Prius Main Forum' started by bwilson4web, Nov 7, 2010.

  1. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Recently we had a discussion about the automatic cabin lights which answered my question. However, this led to another experiment with the 12 V battery.

    HOW TO DRAIN THE 12 V BATTERY

    There are probably several ways to drain the 12 V battery but the method I used:
    [​IMG]
    The overhead lights have three positions:
    1. Left - off preserving the 12 battery and making getting in or out of the car in the dark somewhat brusing.
    2. Center - lights on for ~20 seconds after doors are open which means get in and out before brusing time arrives.
    3. Right - battery drain mode which extends the interval to brusining time to 2-3 days.
    Wait until big light in sky arrives and test and see if the keyfob works. Since this is not zucchini season, it is safe to leave the car unlocked south of Mason Dixon line.

    RECHARGING THE 12 V BATTERY

    The first step is to get in the car and retrieve the Owner's Manual. Turn to the section in the back that covers emergency procedures and read the instructions on jumping the 12 V battery. Unlock the hood and open it up:
    [​IMG]
    Notice the portable Owner's Manual can be brought along to provide a handy reference.

    To the right of the engine compartment is the important fuse box that has the terminal used to charge or jumper the 12 V battery. Per instructions, the recommended ground point is to the left, nearly a meter away.

    With a traditional jump to a lead-acid battery, the recommendation is to attach the ground as far away from the battery as possible and attach it last. This way if there are any electrical sparks, they will be far away from the battery that might have vented some hydrogen gas. However, our Prius 12 battery is located inside the cabin close to the passenger side with an external vent tube attached. Using the recommended ground point actually moves the potential spark slightly closer to 12 V battery vent, ~28.6 cm.

    Access The External Jumper Terminal

    Open the fuse box:
    [​IMG]
    Pushing in on the tab unlocks the cover that lifts up and comes off. I recommend placing this cover over the driver-side windshield wiper so when you forget to put it back on, you will have one last chance to notice and if you drive off, it won't be run over by your car.

    The 12 V terminal is covered by a second, plastic safety cover . . . a somewhat dull red instead of the brilliant red or orange of traditional wiring:
    [​IMG]

    Again, the thumb easily unlocks the cover and it flips over.
    [​IMG]
    A world of hurt could be caused when this terminal is exposed which begs the question: why it is not marked with the brilliant red colors of poison frogs?

    In a dark and foggy night, the dull red might actually be misread as black by unskilled or Prius-hostile roadside assistance staff. They might attach their black ground lead to this terminal and reverse jump the car and blow-out many expen$ive electronics.

    Connect The Charger

    Red to dull-red and black to a local ground but don't plug it in:
    [​IMG]
    The volt ohm meter is optional but shows the batter at 4.8 V. Unplugged, this is the last sanity check before turning on the charger.

    Plug-In The Charger

    Quickly the battery will show 12+ V but you really want to see a steady voltage of 13.5-14+ V before trying to start the car:
    [​IMG]
    If you try to start the car too soon, the electronics will be 'confused' and all sorts of beeps and warning messages will display. My favorite, "must be in Park to start car." Really, go find something else to do for 5 minutes or so while the battery gets a good charge.

    You will need to reset the clock and possibly other settings. My single-beep backup remained enabled.

    Bob Wilson
     
    4 people like this.
  2. Former Member 68813

    Former Member 68813 Senior Member

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    So, basically you are saying you left the cabin lights and discharged the battery?
    What charging current did you use? IIRC, the battery cover talks about 3-4 Amps max. However, if one connects jumper cable, it's going to be much higher.
     
  3. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Prime Plus
    My battery charger has multiple settings:
    • normal or deep discharge - I used "normal"
    • 2 A. - part of the charge
    • 12 A. - part of the charge
    • 75 A. - starting charge, not used
    I tried both 2 A and 12 A but sad to say, it acted as if thermal issues stopped charging midway. So I tried to start it with ~10 V on the VOM and . . . 'it was not a happy Prius.'

    I believe it makes sense to put the charger on and go back in the house for 10-15 minutes. Have a cuppa coffee or other beverage. Watch a bit of TV. Just leave the d*mn thing alone to do what it needs and try to start it after a break.

    Eventually the 'put into Park' message went away; the car started; and I removed the charger and put it away. Then I went back to the car and power cycled it and everything was "OK."

    By the way, the f*ckin' "Smart Key" let the car discharge the 12 V battery. How 'Smart' is that?

    As for those who delight in 'blaming the victim,' B*LLSH*T! Tell me how 'smart' a key is that lets the car become inert. Some engineer needs what I call "reality training." Or better yet, find a young engineer and ask them to make the 'smart key' more intelligent.

    Bob Wilson
     
  4. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    As an aside, let me repeat my views on jump starting:

    1) Never jump start anything with your Prius.

    2) Try to never jump start your Prius, at the first hint of your battery getting 'old', replace it.

    The cost of mistakes while jump starting ($4000) can be an order of magnitude more expensive than just buying a new battery. ($200) If you use a charger, try to get one so polarized so it cannot be attached wrong.

    If you insist on jump starting your Prius buy these before you have trouble.
    http://www.amazon.com/dp/product/B002RRZX06?tag=priuschatcom-20 you object to my biased opinions, we can take it to some new thread, lets not derail this one. I just wanted to warn new owners that jump starting is unwise))
     
  5. Former Member 68813

    Former Member 68813 Senior Member

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    Did it happen to you? What did you fry?
     
  6. Former Member 68813

    Former Member 68813 Senior Member

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    What exactly happened? You left the key near the car and the cabin lights were on?