What Can Draw a Battery Down

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If your vehicle is drawing power from the battery and all of the lights and other electrical components are off, you might have a parasitic battery drain (or draw). Luckily, you can usually find the cause of a parasitic draw yourself. Start by connecting a digital multimeter to the negative battery terminal of your vehicle. Then, remove the fuses one at a time while watching for changes in the multimeter's reading. Once the reading drops, you've found the culprit and can take steps to repair it.

1. 1

   Unplug all devices from your vehicle and make sure no electrical components are on. Turn off the radio, heat or A/C, lights, windshield wipers, etc. and close your glovebox and lighted mirror covers. Engage the emergency brake, turn your vehicle off, and remove the key from the ignition if you haven't already. Then, close all of the doors and the trunk or back hatch so that none of the circuits are activated.^[1]

   • Be sure to remove any cables that may be plugged into your vehicle, like a GPS unit or phone charger, as well.

   Tip: In some cases, you may need to input a security code when you turn on the vehicle after disconnecting the battery, so check your owner's manual for the code before you get started.

2. 2

   Charge your battery fully. In order to accurately detect the parasitic draw, you need to begin with a fully-charged battery. Pop the hood and locate your vehicle's battery. Use a vehicle battery charger to charge the battery to 100%.^[2]

   • Many car batteries are 12.6 volts. You can check the power with a multimeter to ensure the battery is fully charged.
   • If your battery is old or damaged or isn't reading 12.6 volts when fully charged, you may want to replace it before moving on.

3. 3

   Remove the negative battery cable from the negative battery terminal. Find the negative cable, which will be marked with a minus sign (-) and may have a black cover over it. Remove the cover, if applicable, and use a wrench to unbolt the negative cable from the terminal.^[3]

   • Be sure to use the negative, not the positive, cable to test for the draw to prevent electrical shorts!
   • Generally, a 10-mm open-ended wrench is the tool you'll need to remove the cable.

4. 4

   Set up a digital multimeter. The multimeter has both a black wire and a red wire attached to it as well as several different input slots. Connect the black wire to the "com" (common ground) input and plug the red wire into the highest amp input (usually 20A). Set the dial on the multimeter to measure amps.^{[4] [5]}

   • Choose a digital meter than can read up to 20 amps and down to 200 milliamps.^[6]

5. 5

   Attach the multimeter to the negative battery cable and terminal. Place the red lead through the metal circle at the end of the negative battery cable. Touch the black lead to the negative battery terminal.^[7]

   • You can use plastic clamps to secure the leads in place so your hands are free and the meter continues to operate.

6. 6

   Note that you have a parasitic draw if the reading is more than 50 milliamps. There are a few things that constantly draw power in a vehicle, such as the clock on the radio, so it's normal to have a reading between 20 and 50 milliamps. If your reading is higher than that, it means there's a draw and something is using too much power.^[8]

1. 1

   Pull out the fuses one at a time while watching the multimeter reading. Locate the fuse box under the hood. Use a fuse puller to remove the fuses, starting with the ones with the smallest amp ratings and working toward the ones with the highest amp ratings. After you pull a fuse, check the multimeter to see if the reading changes. If it doesn't, replace the fuse and move onto the next one.^[9]

   • Once you've worked through all of the fuses in the fuse box under the hood, check the fuses in the fuse box(es) under the dash. It's best if you have a friend help you with this so one person can pull fuses while the other person watches the reading on the multimeter. If you don't have anyone to help, prop the meter against the windshield so you can read it from inside the vehicle.

   Warning: Disconnect the multimeter before you 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. Then, reconnect the multimeter.

2. 2

   Stop when pulling a fuse makes the reading drop significantly. Removing a fuse may cause the multimeter reading to drop a few milliamps, which is normal. What you're looking for is a significant drop, such as if the reading goes from 3.03 amps to 0.03 amps. When this happens, you've found the electrical circuit that's creating the parasitic draw!^[10]

3. 3

   Find out what's running on the affected circuit. Consult the chart on the fuse box and/or the owners' manual to find out what components are powered by the fuse that's causing the drain. You can also check the wiring diagram for the particular circuit to help you narrow down the problem.^[11]

   • Usually, you can find digital copies of the manual and wiring diagrams online.

4. 4

   Check each device or component on that circuit. Replace the fuse and disconnect each lamp, heater, or electrical device one at a time. Flip all of the switches that correspond to the components as well. Watch for the reading on the multimeter to drop to find out which component is causing the drain.^[12]

   • For instance, say the offending fuse controls the power antenna as well as the radio. Unplug the radio and see if the draw goes away. If it doesn't, unplug the antenna and watch for the reading on the multimeter to drop.

5. 5

   Repair the component causing the draw, disconnect the multimeter, and reconnect the battery. The repair process will vary widely depending on what the problem is, so if you're not sure how to fix the component, hire a certified mechanic to make the repair or replacement. If you can make the repair yourself, check it by ensuring the reading on the multimeter is less than 50 milliamps. Once you're done, disconnect the multimeter and reconnect the battery cable.

   • You may be able to simply flip a switch into the "off" position to eliminate the draw, or you might be facing a more complex problem, such as an issue with a wiring harness.

Add New Question

• Question

  Why is the ammeter connected between the negative terminal and cable instead of the positive side?

  

  The ammeter can be connected to either terminal with identical results with one exception: if you get against a metal object while using a positive terminal, there is potential for a short circuit with a shower of sparks. Use the negative terminal - that is safer.

• Question

  If a new stereo was installed and it wasn't done properly, can that drain the battery?

  

  Yes, if it was connected straight to the battery rather than through the ignition. It should only draw a small amount for the clock when the ignition is off. If you can use the radio with the ignition in the off position, you have a problem.

• Question

  Does a car alarm drain the battery?

  

  Yes, it can. If checking for a drain, the alarm should be the first thing to be disconnected to see if the drain stops.

• Question

  I've pulled every fuse from the box on my BMW and still got something draining my battery totally flat over night? If I remove the negative on the battery over night the battery will hold it's charge.

  

  Are you sure you checked every fuse? Most cars (especially foreign and luxury cars) have multiple fuse boxes. Consult your owner's manual for locations. A 2004 Saab, for example, has a fuse box in the engine compartment and under the dashboard inside the car.

• Question

  Does connecting the negative terminal and getting sparks mean I have a draw?

  

  No. Your car computer, and possibly other components, will activate when the battery is connected. They then go to sleep after a short time, just as they do when you turn off the ignition. A small spark on the connection is normal.

• Question

  I have a 1979 Mercury Cougar XR7. I have a parasitic drain, and don't have a multimeter. I used a test light to determine a short. I tried the fuse pull method, but it was a bust. Any suggestions?

  

  Pull the negative off the battery. Put the test light between the post and the ground wire. If the light illuminates, you have a draw. Use the fuse pull method to find the draw; when the light goes out, you found the draw.

• Question

  I have an 08 Ford Ranger, bought a new battery a week ago. It worked just fine for a day or so, and battery dead again. Took out multi meter (field piece) on the battery meter, set to DC auto, and I got 12.44. Still won't start! I jumped it with another car and it fires right up. Any ideas what is the problem?

  

  I'd try checking your ground wire on your battery. 12.44v is plenty, and when hooking up the other vehicle on jump leads, the other vehicle is completing the circuit.

• Question

  Is it possible that a badly-worn ignition key can cause a battery drain, e.g. if the key can be removed without turning it to the lock position?

  

  Yes it can. Points inside the ignition lock housing can still be closing the circuit, which in turn will leave current flowing, draining the battery.

• Question

  I have a Toyota mini-van with a Bruno scooter lift. If I don't drive the car, the battery dies. The dealer has put in 4 new batteries so far. If I pull the fuse on the lift, the car works fine. What can I do about this?

  

  Put a switch in between the circuit to completely kill the power. Then, when you need to use the van, turn the switch on. Other than that, check your motor for the constant draw.

• Question

  Can Onstar drain your battery?

  

  In older vehicles running analog Onstar, the system will drain the battery because it is constantly looking for a signal. Onstar no longer offers an analog signal, only digital.

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• Don't forget to check inside the cigarette lighter and power sockets. Leaving a phone charger plugged in for a long time can cause a parasitic draw. Also, sometimes coins can fall in the sockets and cause shorts.

• 50 milliamps is a good rule of thumb for max allowable parasitic draw. Anything over 50 milliamps would require further investigation into the exact device which is drawing power.

• Connect the multimeter to the negative battery terminal, rather than the positive one, to prevent electrical shorts.

• Exercise caution when working with your car's electrical system. Protect your eyes and skin with goggles and gloves.

• Consider having this done by a professional. Disconnecting and reconnecting your battery incorrectly can cause damage to your vehicle's electrical system, or it could reset the module, causing the drain to stop, but only temporarily.^[13]

• The information in this article is intended to provide general answers for frequently asked questions about this topic, and may not be applicable to all vehicles. Please refer to your vehicle's owner's manual for details about maintenance intervals and other vehicle specifications. If you are unsure about your ability to perform any repair, we recommend contacting a certified automotive technician to perform the necessary work.

Things You'll Need

• Safety goggles and gloves
• Battery charger
• Wrench
• Plastic clamps
• Digital multimeter
• Fuse puller
• Scrap piece of wood
• Owners' manual

About This Article

Article SummaryX

If you need to find a parasitic battery drain, turn off all of the vehicle's electrical components, engage the emergency brake, and remove the key from the ignition. Next, use a vehicle battery charger to charge the battery to 100%. Then, unbolt the negative cable from the battery terminal with a wrench and attach a digital multimeter to the negative battery cable and terminal. Once the multimeter is hooked up, locate the fuse box under the hood and use a fuse puller to remove the fuses one at a time. After you pull a fuse, check the multimeter to see if the reading changes. If it doesn't change or only drops a few milliamps, replace the fuse and move on to the next one. When pulling a fuse causes the multimeter reading to drop significantly, you've found the electrical circuit that's creating the parasitic draw! For tips on how to correct the problem once you identify the parasitic draw, read on!

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What Can Draw a Battery Down

Source: https://www.wikihow.com/Find-a-Parasitic-Battery-Drain

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