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12v draining....parasitic drain? Help a woman out plz

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by AnnaMerch, Apr 4, 2021.

  1. AnnaMerch

    AnnaMerch New Member

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    Hey.

    ‘I own a 2009 Prius...it has been going strong up until 2month ago...the 12v died...ok no problem I take the old one out and find out it’s the original...I wasn’t surprised....I went to “battery source” and got a new one...

    car drove fine for about 2 weeks and then all of sudden...lights go off and go crazy the whole Shabang...well I figured I must have done something wrong with the install of the 12v...which is practically impossible...I recharged the 12v and put it back in....and now this lovely thing goes dead within +\- 24hrs of not driving it....

    can someone explain to me how to test for parasitic drain? YouTube is a little too confusing on the subject
     
  2. JC91006

    JC91006 Senior Member

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    Maybe you have a bad 12v battery? You should get that tested before looking at other things
     
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  3. edthefox5

    edthefox5 Senior Member

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    Anna did you install it yourself?

    what’s lights go off go crazy the whole Shabang?

    Why are you removing the battery to recharge it?
     
  4. AnnaMerch

    AnnaMerch New Member

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    Because the battery charger is at my father in law’s house across the field and toting it up to our house is more complicated (due to its size) than uninstalling the battery
     
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  5. AnnaMerch

    AnnaMerch New Member

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    So when I first noticed that something wrong I just had parked the car went to my in laws (maybe for 2ish hrs) came back started the vehicle all dash lights came on the dome light came on etc but the car would not go into ready mode...the next day the old battery was done. Therefore I went and replaced it.

    I put the new battery in...it drove fine..and eventually It did the same thing...first I thought it might be something to do with the battery not charging while the car is driving but I am somewhat confident that that’s not the problem since the battery now goes dead overnight with out having driven anywhere.

    I am trying to rule out as much as possible first before calling a mechanic because here in southern Alabama they get scared when they hear you are driving a hybrid. I have time on my hand (somewhat) since my little girl is 11month and happily plays outside close by while I stare at the vehicle with evil eyes.
    I have a great multimeter as well ;)
     
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  6. sam spade 2

    sam spade 2 Senior Member

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    What he said.

    Check the connections on the main battery cables too.
    And check the charging voltage when the car is running (ready).

    If you have the battery tested and they say it is fine.......have them do the test 2 more times a minute apart.
     
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  7. rjparker

    rjparker Tu Humilde Sirviente

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    A cheap meter...
     

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  8. edthefox5

    edthefox5 Senior Member

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    Anna do what rjparker suggests.

    But first lets check your install. Measure right at the battery itself across the 2 terminals.

    Then measure at the front jump point. The front jump should be about .5 volt less due to voltage drop across all its connections and the big cable from the trunk to that front jump point.

    There have been a few reports of the battery brake back up box drawing current as it ages. Its full of capacitors that hold voltage if the 12 volt battery should fail while driving it will provide enough 12 volt power to get you stopped.

    Remember what the battery measures at the front jump point. Then go in the hatch and unplug that brake back up box its the silver metal box just inboard of the 12 volt battery mounted on its side. Just unplug that box then go measure the front jump point and see if the voltage came back up.

    Or compare the current draw readings of rj's amperage test with box plugged in then unplugged.
    As capacitors age they sometimes suffer from ESR and start drawing to much current.

    if you start the car with that box unplugged you will get check engine lights on. Just plug the box back in.

    Post the mileage on your car.
     
    #8 edthefox5, Apr 5, 2021
    Last edited: Apr 5, 2021
  9. pasadena_commut

    pasadena_commut Senior Member

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    The definitive way to settle this question is to put a DC clamp ammeter on the battery cable, either the + one going forward or the short - one going to the body ground. I did that with a UNI-T UT210e, which costs around $50 with shipping. AC clamp ammeters are cheaper but will not work for this measurement. Note, it is essential that the DC clamp be set to zero when it is right next to where you will measure, because it is super sensitive to magnetic fields from all the other currents (or magnets) which might be nearby. That was done on my car in this thread (first page)

    12v draining....parasitic drain? Help a woman out plz | PriusChat

    with the result that there was only a 15mA parasitic draw. However, if a door (or the hatch!) was ajar this went up to 520mA. Note also that one should wait a long while after turning off the car, or a short while after closing a door, before doing the measurement because the car may take a while to shut down whatever background activity is going on. To do this measurement properly one must expose the battery, close the hatch, close the doors, then crawl into the back to measure. The position is not exactly comfortable but it isn't as painful as working upside down under the dashboard with the door sill grinding into one's back.
     
  10. dbstoo

    dbstoo Senior Member

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    You mentioned that your father in law is "across the field". This brings to mind the problem that rodents can cause when they chew through wiring in a car. A visual inspection may show where a wire has been gnawed.

    Checking parasitic drain is simply looking for current flow that exceeds normal amounts. There will be some drain at all times. That's your radio and security system and remote lock activation, etc. But to drain in 24 hours indicates that your drain is probably an amp or more. Once you determine that there is a measurable drain, you can leave the voltmeter in place and move onto the fuse box. Each fuse is marked with it's use. Pull each fuse, one at a time, and check to see if the drain changes significantly. If no change, replace the fuse and move onto the next. If you are lucky it will be a cigar lighter circuit that has something plugged into it. If you are unlucky, it will be something related to one of the many computers.

    If you don't see excessive drain, then it's likely that the battery is faulty. Auto shops and part stores usually have tools to check the ability of the battery to hold a charge. If your FIL has a big honkin battery charger, he may also have a "load tester" to check the new battery.
     
  11. pasadena_commut

    pasadena_commut Senior Member

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    Or turn it around to test for some types of battery faults without a battery tester. Remove the positive cable on the battery and measure the voltage across it. Wait a couple of hours and do so again. If the battery is faulty and will not hold a charge the voltage will have dropped, and since it was not connected to the car at the time, it must be a problem within the battery. This might not be very informative on a battery that was just slightly off, but since yours goes dead in 24 hours you will definitely see a drop if the issue is in the battery.

    The other thing I would worry about is that you might now have two problems. If the car has an issue which discharges the battery too quickly it may have discharged your new one too much so that the battery is now damaged too. You may test the battery and find that it is now faulty, replace it, and in a week or two be right back in the same spot. So if this battery is busted, before replacing it, perhaps jumper in a much heavier battery from another car and check for parasitic currents. But remember, opening the hatch will cause a .5A current even if the car is open, so if you go that way, run the jumper cables in through an open window. I do not recall if opening the hood in order to jumper to that jump point also increases current usage, but it would not surprise me if it did, since many cars have hood open detection switches, and those probably short to ground like the door open switches do.
     
  12. bisco

    bisco cookie crumbler

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    anna, i like your style. all the best