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  • Strange battery drain problem

    Hi guys,
    Couple of months back I had a short circuit in few wires of my 70 series prado (3-door, 1kz-te). Got the wires replaced, but the battery drains completely if vehicle is shut off for more than 36 hours. I checked voltage of battery and each hour, they go down by some milli-volts. The parasitic drain was only about 12 mA.
    I replaced the battery with a new one. Then got alternator checked & got starter motor checked. They are ok too. Battery parasitic drain is still around 12 mA. But again, the battery loses voltage as each hour passes by and after 36-40 hours, it can not start the engine.
    I installed a battery kill switch (cutting the negative terminal connection when the vehicle is shut off), and now the vehicle starts even after 10 days of engine shut-off. So seems it IS a battery drain problem, but why can't the ammeter pick this drainage? How to find it?

  • #2
    Plugging a multimeter in as a shunt (series with your say negative terminal). then you should find a reading on a low Ma scale. Once you find it, start pulling fuses.. Once it dissapears you've found the circuit thats parasitic. rectify as needed.

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    • #3
      12ma shouldn't flatten the battery, you need to put a monitor on it to monitor the drain over the full time, maybe
      there is an intermittent heavy load being applied. You could use something like a cheap watt meter available
      off ebay. You would connect the meter and then see what the total draw has been while the car is garaged.
      Obviously the meter needs to be removed before you run the car.
      HKB Electronics, manufacturer of the Alternator Voltage Booster, Silver 2008 D4D,Lifted,Underbody protection, Alternator Voltage Booster, Tiger Z winch, Lightforce DL, Air Horns, Tanami Drawers, Drop down fridge slide, Outback cargo barriers, Rotronics dual Battery system, Polaris GPS, HF/UHF/VHF, Radio speaker combiner, Long ranger water tank, Diff breathers, Inverter, Snorkel and others

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      • #4
        Originally posted by LeighW View Post
        12ma shouldn't flatten the battery, .
        Maybe the battery is not being fully charged. Are you sure you are starting with a fully charged battery?


        155 SX with dual battery and Polyairs in the rear springs..

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        • #5
          Yes, the battery is charged fully. I checked with a battery gravity (hydrometer) meter and it was 1250 to 1260, which I think is good. Voltage are 12.58 V.
          Piggy : this method doesn't work; only gives a drain of 12mA which goes down to almost zero mA after I remove the fuse that supplies of the cabin digital clock. I removed that fuse couple of weeks back, but still battery was draining after which I installed a kill switch (as a temporary solution).
          LeighW : your are right sir, 12mA is too small to drain the battery. Can you please elaborate more about the watt-meter method? I will certainly try it as soon as possible... going to buy the wattmeter today!

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          • #6
            36-40hours sounds like its not charging.. Is this sitting, or being driven?

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            • #7
              I drive it daily... 80-100 kms. Problem was first identified at weekend. Parked in garage on Friday evening; tried to start the jeep on monday morning and walaaa... Battery flat.
              So then on subsequent weekends i started to remove the negative terminal lead until eventually i put a kill switch.

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              • #8
                A typical watt meter will record amp hours consumed over whatever period you like, just connect it between the positive or negative battery
                post and the battery terminal. don't try and start the car with it in circuit or turn on anything that will exceed its current rating.

                The purpose of using the meter is to see how much is being drawn from the battery over the measurement period as you may have
                something that is periodically drawing current, ie there was a batch of trailer brake controllers that were turning on the brake lights
                of vehicles during the night flattening batteries. If you find here is a parasitic draw then you'll have to start removing fuses as suggested
                above till you find the culprit.
                HKB Electronics, manufacturer of the Alternator Voltage Booster, Silver 2008 D4D,Lifted,Underbody protection, Alternator Voltage Booster, Tiger Z winch, Lightforce DL, Air Horns, Tanami Drawers, Drop down fridge slide, Outback cargo barriers, Rotronics dual Battery system, Polaris GPS, HF/UHF/VHF, Radio speaker combiner, Long ranger water tank, Diff breathers, Inverter, Snorkel and others

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                • #9
                  You haven't got a interior light or glovebox light or something left on? Doesnt sound right at all? Aftermarket alarm? Fridge? Popcorn maker?

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                  • #10
                    Piggy , no I don't have anything fancy installed in the vehicle and always a current draw on 12mA confirms me that I never leave any light or bulb ON.
                    LeighW , thanks for the detailed procedure. I will try it today.
                    Since I don't fully trust the checking method of most workshops about Alternator & Starter motor, so can you please tell if bad alternator and/or starter motor is draining battery, i "should" get the parasitic drain higher, and not 12mA? Right?

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