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Parasitic drain - is 55 milliamps ok?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Charley Gosse, Mar 15, 2023.

  1. Charley Gosse

    Charley Gosse Junior Member

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    My Prius Gen 2 has been losing charge so I did the parasitic drain test and got 55 milliamps. I've read that 20-50 milliamps is ok, anything higher isn't. Is this slight difference - 55 instead of 50 - ok, or should I go ahead and check all the fuses?
     
  2. bisco

    bisco cookie crumbler

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    what has the charge started at in the evening, and what is it in the morning? have you checked it with the neg cable disconnected?
     
  3. Charley Gosse

    Charley Gosse Junior Member

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    Hi Bisco,
    The 55 milliamps is from checking it with a meter with negative terminal diosconneted (meter's black cable to battery's negative stub and meter's red cable to the cable that's been removed from the negative stub).

    I checked the battery using the display's "select vehicle check" and this is what I got. Any ideas? upload_2023-3-16_12-5-53.png
     
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  4. Mendel Leisk

    Mendel Leisk Senior Member

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    55 milliamperes is pretty high; on our 3rd gen I saw 17~20, with sporadic spikes to around 40 (which might be due to the security warning light in dash??). Have you got anything extra plugged in?

    Not sure what you mean by "volts, pressing power once". If I was wanting to check the battery volts, I'd pop the hood the night before (not absolutely necessary, but gives you a completely comatose car for the reading), then in the morning measure the voltage with a mutlimeter, at the jump-point in the under-the-hood fuse box: meter positive lead on jump-point, and negative lead touching solid engine or body metal.

    12.00 volts measured by that method, I'd consider the battery gone. 12.7~12.8 volts would be a 100% battery; down around 12.4~12.5 is getting iffy.
     
  5. Charley Gosse

    Charley Gosse Junior Member

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    Hi Mendel,
    In terms of the steps I followed to check my battery voltage this morning before and after driving, I followed this video (<=that is a link to it on YouTube), it's titled "check your 12v Auxiliary Battery self test (Toyota Prius)." It uses the Prius's dashboard display to get readings.

    I will follow what you recommend to check the battery tomorrow morning ("measure the voltage with a multimeter, at the jump-point...") but I'm not sure what you meant about popping the hood tonight. I should just pop the hood and leave it up overnight? Is there anything else I should do?

    My yellow-top optima battery is just over 3 years old so it is out of warranty. I thought maybe it needed to be re-charged so I took it to a local advanced auto parts store and they tested it and said it's fine. I put the battery back in my car, made sure verything was off and checked the milliamps with a meter and got the 55 milliamps.

    I then found that this light, the one in the photo, was switched to "on" but it wasn't lit because the mirror on the visor wasn't slid open. I turned it off, re-checked the battery with the meter and milliamps dropped slightly to 52. Note sure if this is relevant.
    IMG-0581.jpg
    I have not yet done the part of the parasitic draw test where you remove each fuse one-by-one to see if milliamps drop. Should I do that? Is it possible to do that test by attaching the meter to the under the hood battery terminal or do I need to do the test right at the battery?
     
  6. mr_guy_mann

    mr_guy_mann Senior Member

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    Assuming that you are testing draw at the 12V, have you used a tool to "close" the tailgate latch?

    Do so and close all doors. Let the car sit 20 minutes then check the reading. 50mA is "OK" for a luxury car with a big battery. A Gen2 is usually 15-20mA.

    If there's any aftermarket stuff (stereo or remote start-alarm) then all bets are off.

    Posted via the PriusChat mobile app.
     
  7. Mendel Leisk

    Mendel Leisk Senior Member

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    If you pop the hood in the morning, just the action of getting in the car to do that uses some juice. Less if you go in through passenger door, reach across. This’ll drop the battery voltage, a minor amount though.

    but if you pop the hood the night before (assuming you have secure enough parking situation) , by morning voltage will have stabilized. At least that’s @bisco’s theory.

    yeah using the dash display to read voltage, it’s dropped, by turning the car on; you don’t want that.
     
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  8. pasadena_commut

    pasadena_commut Senior Member

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    Those rows are, top to bottom: ACC, IG-ON, and READY. There is a current draw from the battery in the first two cases (assuming all the doors are closed, that is ~2.3A for ACC, anywhere from 9A to well over 20A in IG-ON, depending on what is running,). That current draw will drop the voltage of the battery some, and it will recover when the load is removed. In READY everything you see is just the inverter output voltage.

    Your battery has quite a low SOC but the voltage drop from ACC to READY is much less than the one on my screwed up 12V which has only about 12.5 Ah of capacity instead of the rated 46Ah. I believe some early Prius gen II years might also have had a 36Ah battery, or thereabouts. So my guess is that your battery is low, but its capacity and internal resistance may still be pretty good.

    In any case, I suggest the OP charge the battery at not more than 4A until it is at 100% SOC. Wait overnight, and measure the voltage under the hood as Mendel Leisk suggested. Then again using ACC. Do that for a few days and see if it will hold charge.

    To see roughly what the battery capacity is, charge the battery to 100% SOC and let it sit overnight. Measure the voltage under the hood with the car off. Then go to IG-ON, all doors closed, all lights off, AC, defroster, and radio off, cabin blower set to 3rd highest position. Wait 15 minutes. If your car is like mine that will pull very close to 5Ah out of the battery (20A load for 1/4 of an hour). Turn the car off, pop the hood, exit the car closing all the doors, and wait 20 minutes. Measure the voltage again. Look up the two voltages on an AGM SOC chart and subtract. Let's say that you see .9 - .6 to give .3 difference, then the capacity of the battery is 5Ah/0.3 = 15Ah. On a perfectly healthy battery it should only drop around 0.11 SOC.

    I don't recommend taking the Prius battery to an auto supplier for a conventional load test. Apparently these batteries can have terribly low capacity and still pass those tests. Mine did. I estimate it would have to lose about another 2/3 to 3/4 of its remaining capacity to fail, and I don't really want to be driving around with a 12V that weak.
     
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  9. Mendel Leisk

    Mendel Leisk Senior Member

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    A lot of battery retailers (and the the dealership, though they'll charge for the test) have electronic load testers. You can pick up a DIY level tester of that ilk for $50~60 USD. Solar BA9 is the current itteration of the the BA5 I'm using, works well. You enter your battery type, CCA spec, and run the test. It tells you the as-tested CCA, and gives a verdict, either pass, pass-but-recharge or fail.

     
  10. bisco

    bisco cookie crumbler

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    Agree with everyone above, you need a full charge, then see what it has dropped to overnight.
    But if 55 is way too high, you’re gonna have to chase the fuses regardless
     
  11. Charley Gosse

    Charley Gosse Junior Member

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    Mendal, I followed your directions, hood up overnight, and got 12.38 v this morning, so this is below the “iffy” range, should I replace it? If do, is there a brand/model you recommend? Current 12v batt is optima yellow top, just past it’s 3 year warranty.
     
  12. Charley Gosse

    Charley Gosse Junior Member

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    I tricked the hatch into thinking it was closed and waited 20 minutes and tested for parasitic draw. It's still at 55 milliamps! Just to make sure I did this test correctly, here is the process I followed. I did this at the 12v battery, itself, not at the jumping lug under the hood, and I was using the process from wikiHow, an image from which I have atatched below.
    1. I removed the negative lead from the 12v battery
    2. I touched the 12v battery's negative contact point with the negative lead from the multimeter and while doing that
    3. I touched the previously removed negative battery lead with the multimeter's red lead
    I had not removed my smartkey fob from the area but I am assuming that doesn't matter.

    I understand that I should now
    a. pull out each fuse one at a time beginning with the fuse box under the hood while reading the multimeter and see is there is a drop
    b. then, if no drop is seen, continue this process with the fuses under the dashboard. Ofcourse, I will disconnect the multimeter before I open the door to check the fuses under the dash, disable the door switch by clamping a piece of scrap wood over it so it remains depressed, and then reconnect the multimeter and continue to look for a drop.

    Please confirm my process. I'm waiting out the rain right now.
     

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  13. mr_guy_mann

    mr_guy_mann Senior Member

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    Get the smartkey more than 10 feet away- or turn the system off. If the system is turned on and the key is in proximity , the car will be "awake" to some extent.

    Might have to "close" the door latches if you want to check draw with the door open.

    Posted via the PriusChat mobile app.
     
  14. Mendel Leisk

    Mendel Leisk Senior Member

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    You charged it beforehand too? Yeah that's low. Not crazy low, but I'd start shopping, and have a jump pack in the car.

    FYI:

    I've also got an Optima Yellow Top, installed September of 2015. Within a year or two of installing both my wife and I were retired, and our use of the car (2010 Prius) dropped off. Then with the advent of COVID, doubly so. Currently we're lucky to do 3K kms yearly, driving as little as once a week.

    In that first year or two, we would be going for drives, "just to keep the battery healthy", and then I started thinking that's a little absurd. So I installed a quick-connect harness that came with my CTEK 4.3 charger, installed the charger on the wall adjacent to the car's engine bay, and just started plugging it in, any time the car was sitting idle. So pretty much round the clock.
     

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    #14 Mendel Leisk, Mar 17, 2023
    Last edited: Mar 17, 2023
  15. Mendel Leisk

    Mendel Leisk Senior Member

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    Next time I probably won’t go with Optima Yellow Top; I’ve heard it’s higher CCA comes at expense of Amp Hours.
     
  16. pasadena_commut

    pasadena_commut Senior Member

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    If the battery was fully charged the night before then that is terrible, it implies a voltage drop from 100% SOC to 12.38 V which is about 75% SOC.

    https://learnmetrics.com/agm-battery-voltage-charts-12v-24v-deep-cycle-battery-voltage/

    With just the 55 mA load, for 10(?) hours, which is just just 0.55A. It is a 46Ah battery, so it should have taken about 11Ah to drop that much.

    On the other hand, if you did not charge the battery the day before it could be fine. 75% SOC might just reflect insufficient driving time. The battery in this car never charges at more than 4A, so it takes a lot more driving to fully charge than does a typical car battery. Unfortunately, as has been explained elsewhere on this forum, by I don't recall who, this isn't a deep discharge battery, so all the time it spends significantly below a full SOC damages it, slowly but surely. This is one reason some people are using deep discharge sealed batteries in their Gen 2's. Despite the potential safety hazard from having that sort of battery in the cabin.
     
  17. CR94

    CR94 Senior Member

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    For batteries generally, and for a given physical size, higher CCA tends to come at the expense of deep-discharge durability. I thought, at least as of a few years ago, Optima offered a choice of high CCA or deep-cycle capability---the latter being more appropriate for Prius usage.
     
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  18. bisco

    bisco cookie crumbler

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    i wouldn't buy a battery until you find the problem, might be a waste of money
     
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  19. Charley Gosse

    Charley Gosse Junior Member

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    This morning I did the complete parasitic drain test. At the 12v battery, I removed the negative lead, attached the voltmeter's black lead to the negative contact point, meter's red lead to the previously pulled negative lead, and got 58 - 59 miulliamps, like before. I then pulled and put back each fuse working through the fuse box under the hood and then the one under the dash and nothing changed, the reading stayed at 58 to 59 ma so I haven't found whatever it is that is causing the parasitic drain. The key fobs were 30 feet away and the car had rested for 30 minutes, all doors locked, no activity whatsoever. Not sure what I am doing wrong.

    In a previous post I said that my 12v Optima YellowTop battery is 12.3v in the morning. I don't have a battery charger so should I let the car sit for 12 hours in ready mode to top up the 12v battery or can anyone suggest an appropriate battery charger for this type of battery?
     
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  20. JohnPrius3005

    JohnPrius3005 Active Member

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    I use Foxsur bat chargers. If you're interested I can give you the model numbers I like. The most important thing I've found is to charge the bat when it's disconnected. Of course this requires a secure place to park because you have to wedge the back hatch open or access the car with the key and then crawl back and work on the bat.