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12v battery issue == HELP!!

Discussion in 'Gen 2 Prius Technical Discussion' started by ruggb, Dec 9, 2019.

  1. ruggb

    ruggb Junior Member

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    HELP! 12V Mystery. Battery was fine, HV battery was charged. Been working on another issue with a TS adapter. All of a sudden I get the BIG RED TRIANGLE OF DEATH. Can't do anything. Check 12V == 3Volts.
    Can,t open rear doors or hatch. Tried connecting charger to fuse box terminal and it is pegging my ammeter == >10Amps. Did not leave it connected. When I did connect it things clicked and maybe a motor ran, but why it is drawing so much current??? Voltage appears to go to 9V when I connect charger == obviously trying to draw more current than charger is capable of.
    Now what do I do? How do I get to battery to disconnect it?
     
    #1 ruggb, Dec 9, 2019
  2. bisco

    bisco cookie crumbler

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    crawl in the back with a flashlight. below the deck at the center of the hatch door is a little cover you pry off and unlock the hatch with your fingers

    can't help with the power draw, sorry
     
    #2 bisco, Dec 9, 2019
  3. SFO

    SFO Senior Member

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    Almost sounds like you depleted the 12v while "working on another issue".
     
    #3 SFO, Dec 9, 2019
  4. ruggb

    ruggb Junior Member

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    I managed to crawl in from the front (btw, I am 77 yo) and disconnect the neg batt terminal. Now I need to crawl back in and measure the volts.
    Is there a manual release for the hatch or the back doors. Apparently the child lock is active on them.

    Apparently, there is a large load on the 12V, but it just happened as I was not doing anything with the TS except looking at things with it on but not running.

    Any ideas?
     
    #4 ruggb, Dec 9, 2019
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  5. ruggb

    ruggb Junior Member

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    The batt voltage open circuit is 9V and 7V when connected, but there is 234KΩ resistance + to - which isn't much of a load. The battery was replaced after 128,000 miles and has about 60,000 on it now.
    still can't find hatch release.
     
    #5 ruggb, Dec 9, 2019
    Last edited: Dec 9, 2019
  6. bisco

    bisco cookie crumbler

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    look for a small 2 x 4 cover at the bottom of the hatch door in the center

    how old is the 12v? it might be toast. you'd have to charge it up and test it to find out.
     
    #6 bisco, Dec 9, 2019
  7. ruggb

    ruggb Junior Member

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    thanks, == found it. They could make it just a little smaller, then I would have needed my mag glass along with the flashlight.

    The aux battery is charging at about 2 Amps. Have no idea what was drawing the current to discharge it. Maybe I will find out when I reconnect it.

    It only has 60,000 miles on it, I replaced the orig at 128,000 along with the HV battery.
     
    #7 ruggb, Dec 9, 2019
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  8. royrose

    royrose Senior Member

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    It is not just a matter of miles. How many years old is it?
     
    #8 royrose, Dec 9, 2019
  9. ruggb

    ruggb Junior Member

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    it is OMG, how time flies == the first one had a cell or two bad at 6 years, in Jan 2013, so THIS one is 7 YO.
    Maybe I need a new one. No indication it was bad previously, Unless this is somehow causing mt P1121 DTC.
    Can't see how. but b4 I got to it and disconnected it something was drawing over 10 Amps.
    That wouldn't be good for this battery.
     
    #9 ruggb, Dec 9, 2019
  10. TMR-JWAP

    TMR-JWAP Senior Member

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    Your depleted 12v battery was probably drawing most of that initial current. When you connected to the underhood charge point, the old battery was at 3 volts. You connected a 12+volt battery/charger to the underhood charge point, which is really just a 10 ft long heavy gauge cable going directly to the positive terminal of the battery. It was trying to charge the old battery.
     
    #10 TMR-JWAP, Dec 9, 2019
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  11. ruggb

    ruggb Junior Member

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    I have a control on the charger and I turned it all the way down so it should have reduces the current. It did not. When I put it on the battery only I was able to set the current to 3 Amps. Something was drawing that +10 Amps other than the battery.
     
    #11 ruggb, Dec 9, 2019
  12. ruggb

    ruggb Junior Member

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    Thanks guys == Guess what == turned out it was my fault. While I was working on it I didn't realize the headlights were on. That apparently drained the batt. All charged up and it appears to be good. Thanks.
    ​
     
    #12 ruggb, Dec 9, 2019
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  13. edthefox5

    edthefox5 Senior Member

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    You were probably in acc mode when you had TS connected.

    Acc mode is achieved by pushing the start button without holding down the brake. Since engine won’t start it will not charge anything. You killed that battery.

    There’s a little red cover over the top of the positive terminal on the 12 volt battery. Remove that cover there’s 2 wires connected to that black plastic assy big one is main power line that goes to the front jump bolt the other is a 12 volt sensing wire for the inverter. To remove compress white clip and pull the cables out.

    This disconnects the 12 volt battery from the car. Do this instead of unbolting the nuetral.

    Ps
    Usually killing the 12 that way will damage it or cause it to not perform 100 percent.
    As you experienced a dead 12 is a pia.

    Prove me wrong with this test:

    With car off measure 12 volt voltage at front jump point to ground. Write that down.

    With car off turn on headlights on high beam for exactly 5 minutes.

    After 5 turn off headlight and measure 12 volts again with car off.

    If the voltage has dropped more than 2 volts from first volt check it’s toast and will not survive even a minor load or incapable of full charge. A healthy 12 bolt should not drop 1 volt after this minor load test.
     
    #13 edthefox5, Dec 10, 2019
    Last edited: Dec 10, 2019
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