Fix Battery Drain - Amp Draw Diagnostic and Testing Tool Reviews

How to Find and Fix a Parasitic Battery Drain

You walk out to your car/truck, turn the key, and you hear the glorious click-click noise. Overnight, you’ve had a battery drain, but you didn’t leave the lights on. Who knows where the battery cables are, and you haven’t recharged your jump-box since the last camping trip. Yeah, we’ve all been there. We’ll show you the simple way to find a parasitic battery drain; in other words, we will find what has caused your dead battery.

Why read when you can watch the video? You may want to check out our How To Find a Parasitic Battery Draw Video for step-by-step instructions.

Southwire Multimeter - 14090T

Set to Amps DC – Pay Attention to Wire Leads

Tools Needed: 

  1. Multimeter – must have an Amp (DC) reading – at least 10 Amps (We used the Southwire 14090T)
  2. 8mm, 10mm, 7/16, or 1/2″ Wrench/Socket – to remove your battery terminal
  3. Needle-nose pliers or Fuse-puller – for removing fuses from the fuse panel/s
  4. Zip-ties or small clamps


What is a Parasitic Battery Drain?

It doesn’t involve parasites in your battery, so that’s a good thing. No need for HazMat suits, yet! A parasitic battery drain is just something that consistently and continually drains your battery. This could be a faulty relay, a headlight/dome-light switch, alternator, or any other electrical gremlins. Taking your car to a mechanic with an “unknown” culprit can cost you big bucks as well. Most mechanics don’t enjoy diagnosing electrical issues.

Milwaukee Tool Ratcheting Wrenches

How To Diagnose the Battery Drain

You should be able to diagnose your battery drain issue within a few minutes. An extra helper may help with this project, but it’s not needed. Keep in mind, depending upon your vehicle, you probably have more than one fuse panel. Most vehicles have at least one fuse panel under the hood, and another inside the passenger area. Some foreign cars have multiple fuse panels inside, in different areas. You may want to check your owner’s manual or check one of the forums.

Parasitic Battery Drain

Remove Negative Cable

Step 1: Remove Negative Battery Cable

Parasitic Battery Drain Neg Cable

Negative Cable Removed

Using the correct wrench or socket, remove the negative battery cable from the battery post. In our case, we were working on a 2000 Ford Explorer, so the battery terminal used an 8mm bolt. You can perform this test/diagnostic by using the positive or negative cable, but using the negative is much safer. Grounding a negative wire to ground is not a problem; however, grounding the positive could destroy electronics, including your multimeter.

Step 2: Check the Draw Across the Negative Cable and Battery Post

Turn on your multimeter and select the Amps (A) and make sure it’s set for DC (Direct Current). You should see a symbol like a solid line, with dashes underneath. You Don’t want AC (~), this is for your home’s electric. You will probably have the option for Amps or mA (milliamps), so choose the Amps to start with, preferably 10A or 20A. Make sure your wire leads are in the correct location, on the multimeter. There should be a diagram on the multimeter, showing you where to put the test lead wires.

Southwire Multimeter Test Leads

You’re going to be putting your multimeter in series of the battery drain or current draw. This means the current draw will be passing through the multimeter. In our case, we had a 4.4 Amp draw, so that power was flowing through the multimeter. Be certain your leads and dial are in their correct locations.

Parasitic Drain Zip Tie Leads

Place one of the wire leads from the multimeter (it doesn’t matter which one) on the negative battery post and the other on the disconnected battery cable. You should see the multimeter display the number of Amps that are actively causing your battery drain. Use zip ties or small clamps to keep the multimeter leads connected to the battery terminal and battery wire.

Tip: A normal operating vehicle will have about 50 milliamps of Amp draw on the battery.

Another Great Video: Best Drill Bits

Our Best Drill Bits Video

Step 3: Remove and Replace Fuses

Start with your underhood fuse panel. Make sure that you can see your multimeter while you pull fuses. Use your needle-nose pliers or a fuse puller to remove and replace fuses, until you see the Amps on the multimeter drop. Be careful that each fuse goes back into the correct location.

Parasitic Drain - Remove Fuses

Remove Fuses

If you get through all your underhood fuses, then move into the inside fuse panels. This is where an extra person can help, they can monitor the multimeter while you pull fuses. If you don’t have help, the leads on the multimeter should be long enough for you to place the multimeter face-down on the windshield.


Step 4: Isolate and Fix the Issue

Once you pull the fuse that is the culprit, then you can fix the issue. In our case, it was the Alternator/Voltage Regulator that was pulling more than 4 Amps continually, which turned out to be a faulty alternator. Once we removed this 30A fuse, the Amp draw dropped to 0.2 Amps, which is still more than typical. We also found a secondary draw with the Interior lamps relay/switch. Removing both fuses dropped our Amp draw down to almost nothing.

We replaced our alternator, and we’ll replace the interior switch another time.

Fix Battery Drain - Issue Found

Step 5: Replace Negative Battery Cable

Now that you have the issue/s fixed, you can remove the zip-ties/clamps from the multimeter leads and replace your negative battery cable. You should be good to go, and your parasitic battery drain has now been fixed.

Notify of

Newest Most Voted
Inline Feedbacks
View all comments
David S
David S
3 years ago

You forgot one very important step. Most cars have multiple modules, (computers), in them now, and some of those modules stay energized for up to 10 minutes when the battery is disconnected. This is especially true for the SDM, (Sensing and Diagnostic Module, aka air bag module). You need to wait for these modules to power down before checking for a parasitic draw, otherwise you may diagnose a faulty module when you remove the fuse for that module only to find out that the replacement module is doing the same thing because you aren’t allowing it to power down.

2 years ago
Reply to  David S

That’s exactly what a guy said on the Corvette forum. Fortunately my car has been sitting in my garage for a week lol! Thanks for the reminder

2 years ago
Reply to  Scott

when connecting the meter in series to the battery it still turns on the computer, ECM, BCM and it runs a system check then turns off, even if the car has been sitting.

David Crandon
2 years ago

I am trying to diagnose a 0.4amp parasitic drain on a 2004 Honda S2000. I was using the conductive clamp on my MM though around the bundle of wire coming off the positive end of the battery. One question though…is each and every electrical component connected to a fuse? There are no exceptions?

2 years ago

Awesome! Thank you! Mechanic love having people come in with electrical problems. I’m doing this today and crossing my fingers that I find the issue. How many times can a battery be drawn down to where it damages the battery. I’ve had this bite me about 5 times. I should have left my trickle charger on 24/7. The thing is the battery takes forever to charge with the trickle charger. I suppose the parasitic drain is slowing it way down. My battery was just over 11 volts when I threw the trickle charger on. It’s been trying to charge the… Read more »

2 years ago

I have 03 Infinity G35 Sedan, The battery drains over night. Pulled all the fuses no problems; Checed to see if there was a draw on the battery ,no draw. Change the alternator and battery. A certified Nissan mechanic ran all the basic test and found ,no draw from the battery,no bad fuse,is no drawing fuses. I am at my wits end please ,thank you. Any other suggestions are well appreciated.

1 year ago

Thanks for the info! I was able to find the battery draw using this method, but after putting in a new fuse the problem still remains. When I remove the new fuse it drops to 0.05 amps, but when I replace it we jump up to 0.4 again. Any tips on why a new fuse wouldn’t fix it?

Ferrel Bird
Ferrel Bird
1 year ago

Great content even though I was sure I could find the problem myself because I love electrical troubleshooting work. I was stumped on this one! Thanks so much for the help.

J. Berman
9 months ago
Reply to  Tim Johnson

RE: 2007 Ford Fusion. When initially connecting meter, the draw is 2.0Amps. Remaining connected meter then drops to 0.64A within 10 minuets. Pulled fuses but could only find fault when pulling Master Circuit (60A) fuses. Could a bad diode within the alternate be the problem. Any suggestions would be appreciated. Thank you

Phil Richardson
Phil Richardson
9 months ago

Made a check and first the multimeter showed 330ma but quickly changed to 20ma. Odd I thought. Did this several times and kept getting the same readings. Car has not been used for 3 months with no battery connected.

7 months ago

Hi, I have a parasitic drain on my battery, it goes down to 0 vdc over night. I followed the instructions, when I go from the positive to the negative lead it shows no drain. Any ideas?

6 months ago

I did the required testing and found nothing regarding a drain from any of the fuses. However when I connected the negative cable to the battery post the battery immediately started to drain. Any ideas? Thanks

David Brubaker
David Brubaker
3 months ago

I have a drain in my Ford F-150, have been looking into it for a week now. I saw this video about testing it with a multimeter so I bought one, and I did the test on the negative side of the battery. My settings were 10A DC test; but it blew the 10A fuse in my multimeter when I tried the test. It first arced twice when I tried to get the reading, very small arcs, then I wasn’t getting any readings and I tested the fuse and it was blown. Any thought as to why it would have… Read more »