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Parasitic Draw: Why Does My Battery Keep Dying?

A woman wearing gloves looking under a car's hood

Parasitic draw is a fancy way of saying there’s something constantly draining your battery, causing it to die prematurely. It’s why your battery dies if you accidentally leave your headlights on or don’t shut the car door all the way, causing the overhead light to stay on all night.
Battery Clamp
While those culprits are easy to diagnose, sometimes the reason your car battery is experiencing parasitic draw isn’t quite so obvious. Many unexpected things can cause your battery to drain even when you’re not driving your car. Here are a few tips for avoiding battery drain and a potentially dead battery.

How to Test for Parasitic Draw

You can test to see if your battery is draining using a multimeter. These inexpensive devices connect to your battery and can show you if the battery is being drained even when you think everything is off. Not only can they confirm the problem, they can also confirm that you’ve eliminated the problem and the drain has stopped.

Check the Easy Stuff

Leaving your headlights on overnight or not closing the car doors properly will probably result in a dead battery. If those aren’t the cause, then check a few less likely, but still common, possibilities.

A slightly open trunk, or even one that doesn’t latch properly, can illuminate the cargo light. The same is true of the glove box. These might not run your battery overnight, but they will cause it to drain over time, shortening your battery life. Make sure these things latch securely and replace or repair loose latches.

Avoid Accessory Mode

When you turn off your car’s engine but leave it in accessory mode, it’s not completely off, so you can still use some features such as the stereo. It’s not uncommon for people to do this when they don’t want to waste gas while they sit and wait for an appointment or for someone they’re picking up to come out to the car.

While this is fine on occasion, it does drain your battery. Newer cars will often warn you that you’re using up the battery after leaving it in this mode for too long. It won’t cause a problem now and then for short intervals, but if you do this all the time, you’re creating a parasitic draw that’s not good for your battery’s health.

Be Aware of Aftermarket Accessories

Even if your new stereo sounds amazing and your new alarm prevents anyone from stealing the car, these aftermarket accessories could be draining your battery. An easy way to check for parasitic draw from an aftermarket accessory is to disconnect it and see if the issue disappears. Let the installer know there’s a potential issue, so they can double-check the system and see if it’s the source of your problems.

While batteries do need to be replaced over time, if yours is constantly in need of replacement, then there’s likely a battery drain. A little sleuthing will uncover the problem and ensure a healthy battery life.

Check out all of the batteries available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on car batteries, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.


Nicole Wakelin View All

Nicole Wakelin covers the automotive industry as a freelance journalist for a variety of outlets. Her work includes news pieces, podcasts, radio, written reviews, and video reviews. She can be found in The Boston Globe, CarGurus, BestRide, US News and World Report, and AAA along with lifestyle blogs like Be Car Chic, The Other PTA, and She Buys Cars. She is active on social media with a large following on both Twitter and Instagram and currently serves as Vice President of the New England Motor Press Association.

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