Parasitic Draw Test with a Multimeter
It could be anything from a dimming dome light staying awake or a glove compartment switch sticking on, to faulty alarm wiring, but a car battery may experience significant drain long after the engine has been turned off, which is known as parasitic draw and can lead to a flat.
What You’ll Need
A digital multimeter, rather than an analog one, is best for this test; you’ll need a milliamp range for higher resolution to detect minimal current draw, and it’s best to stick with a brand name, though you don’t have to go with a top-of-the-line Fluke model.
Before starting, make sure the battery is fully charged and that all doors are closed, the radio is turned off, and all accessories are disconnected. It is always best to do a parasitic draw test from the negative side to avoid accidentally shorting. Avoid starting the engine or turning on the headlights as this will likely blow a fuse in the multimeter.
PARASITIC DRAW ESTABLISHED
When the multimeter display drops to a nominal mA draw, it’s time to look for faults. The tried-and-true method is to start pulling fuses to see which circuit is the culprit, then repair or replace the item and test again.
Parasitic Draw Test on Newer Cars
Electric mirrors, heated memory seats, GPS, trackers, and a slew of other gadgets can make parasitic draw testing with a multimeter a pain. Some of these systems are interconnected, exacerbating the problem. Even car keys indirectly cause current drain.
Old vs New Method
There’s no need to remove auto fuses or disconnect the battery because they have open test points on them. Different size fuses will show a different voltage drop; for example, a 10A fuse with 1A flowing through it might show a voltage drop of 5mV.
Drive the car and operate all circuits (wipers, heater, seats, windows, GPS, lights, sat-nav, etc.) before returning and removing the key. Consult the manual for information on how long the various systems take to sleep.
Key to Better Battery Life
The key to a long battery life is to avoid parasitic draws and keep the battery charged above 12.4V. Vehicles that are only used occasionally are more prone to losing charge, which leads to sulfation, which compromises performance and longevity. Those that are driven daily benefit from the alternator, which keeps the battery charged.
Parasitic draw on one’s vehicle can be a nightmare, and it frequently occurs at inopportune times; however, it doesn’t have to be, and it is entirely within the realm of the layman, as long as a multimeter is available. See how to check battery charge here.
Choosing a Multimeter
For a parasitic draw test with a multimeter, all you need is a basic device that can test amperage and has an auto ranging mode. INNOVO makes decent multimeters for automotive tasks, such as the 3340 or the less expensive 3320.
How do you check for a parasitic draw on a car battery?
Remove the negative terminal from the battery and connect the test light to the post and ground wire. If the light illuminates, you have a draw. Use the fuse pull method to locate the draw; when the light goes out, you’ve located it.
What is an acceptable amount of draw on a car battery?
A normal amount of parasitic draw for newer cars is between 50 and 85 milliamps, while a reading less than 50 milliamps indicates an electrical issue that should be addressed by a mechanic. Anything above these amounts indicates an electrical issue that should be addressed by a mechanic.
How much should car battery voltage drop overnight?
When you measure the voltage right after a drive, it should be closer to 13.2, and it should drop to 12.7 within a few minutes as the chemical reactions in the battery slow and stop when you stop charging it.
How do you know if you have a bad battery?
The following are the most common symptoms of a bad battery:
- The battery light is illuminated on the dashboard. The engine cranks slowly when starting. The vehicle requires frequent jump starts. The engine clicks when you turn it. The lights are dim.
How do I check for a battery drain?
How to Recognize and Treat Battery Drain
- Step 2: Check the Draw Across the Negative Cable and Battery Post.
- Step 3: Remove and Replace Fuses.
- Step 4: Isolate and Fix the Issue.
- Step 5: Replace Negative Battery Cable.
How much parasitic draw is acceptable?
In fact, we recommend a maximum draw of 25 milliamps, with anything over 100 milliamps indicating an electrical problem that must be addressed.
Why should a battery not be fast charged?
The purpose of a standard battery charger is to send a constant voltage to the battery until it is turned off. Charging a battery too quickly can damage it, reduce its performance capacity, shorten its life cycle, and even cause it to catch fire.
What can drain a car battery instantly?
7 Things That Will Deplete Your Vehicle’s Battery
- Something is causing a “parasitic draw.”
- Your battery connections are loose or corroded.
- It’s extremely hot or cold outside.
- The battery isn’t charging while you drive.
- You’re taking too many short drives.
How do I check what is draining my iPhone battery?
How to check the status of your iPhone’s battery
- Launch Settings from your Home screen.
- Tap on Battery and wait for it to populate.
- Tap on the Show Activity button to see a breakdown of foreground and background power usage.
- Tap on Last 10 Days to see power consumption over time.
Can a bad ground cause battery drain?
Your vehicle’s charging system relies on a good ground; if the ground wire is damaged, the battery will not be charged. Of course, problems with your alternator or the wire that connects the alternator to the battery could also be the cause of a dead battery.
What’s draining my car battery overnight?
Parasitic drain can be caused by a variety of factors, the most common of which is leaving headlights, glove box lights, or cabin lights on overnight. It can also be caused by faulty fuses, bad wiring, or improper installation of a new car battery.
Can a blown fuse drain car battery?
Blown fuse = dead battery? A fuse blows to prevent current from flowing through a circuit; therefore, a blown fuse cannot drain the battery. take the battery in to be checked; it could simply be a bad battery.