Like tires and brakes, car batteries also wear down over time and require replacement. But what if you have a newer battery that’s losing its charge? It could be defective, or it could be getting drained by a malfunctioning or improperly wired element of the vehicle. Fixing this issue is crucial to avoid frustrating jump starts or being stranded with a car that won’t start. Ahead, learn how to figure out what’s draining your car battery — and how to fix it — with car expert Justin Dugan of American Muscle.
Signs Your Car Battery Is Being Drained
The main sign that your battery is draining rather than dying is “a car that has difficulty starting after sitting for a relatively short period of time, although the battery appeared to be functioning well prior to this,” Dugan says. For example, if you park your car on Friday and need to jump-start it on Monday, then again a few days later, this is a pattern that indicates a draining battery, which can have several causes.
While you may also notice dimmer-than-normal interior lights and a slow engine crank, these signs alone do not indicate a drained battery. It’s a battery that keeps dying and needs repeated jump-starts, likely paired with these signs that point to a drained battery. “Repeated dead-battery failures are typically indicative of either a problem with the vehicle’s charging system or the wiring configuration, and not solely due to a weak battery,” Dugan says.
Common Causes of a Draining Car Battery
Accidental
Leaving headlights, interior lights or the radio on while the engine is off is a common cause of a drained car battery. A simple jump start should solve the problem.
Parasitic draws
A more complex cause is parasitic draw, where an element of the car continues to draw power from the battery even when the engine is off. “The actual cause of battery drain is not necessarily the battery itself, but rather a component that has failed within the car and is continuing to draw power, or an accessory that was wired continuously to the battery instead of being tied into a keyed ignition circuit,” Dugan says.
Accessories like dash cams, sound systems and custom lighting can lead to drain if connected directly to the battery. Alternatively, a faulty ignition switch, door sensor or relays can fail to disconnect electrical components from the battery when the ignition turns off.
Alternator issues
A faulty alternator will fail to charge the battery while driving, leading to repeated jump starts. Also, failing alternator diodes can lead to alternator backfeed, where electricity flows backward from the battery, also causing drain.
How To Diagnose What’s Draining the Battery
Parasitic draws
“The diagnostic process is primarily about being systematic and deliberate in eliminating potential sources of the drain, versus making random guesses,” Dugan says. “Eliminate all the obvious expected draws, such as clock memory or courtesy lights, and then systematically go through the remainder of the system.”
Use a multimeter to identify the circuit draining your battery, then focus on the components in that circuit.
- Turn the car off and let it sit for 15 to 20 minutes with the doors closed and lights off.
- Remove the negative charge cable from the battery.
- With your multimeter set to DC, connect the black multimeter lead to the battery’s negative charge cable and the red multimeter lead to the negative post on the battery.
- With the multimeter in place, remove fuses one at a time until the amp reading drops, indicating the source of the drain.
“This will give you information regarding whether you are dealing with a defective component, an alternator backfeed or a device that has been improperly wired to a wrong source of power,” Dugan says.
Alternator
If you did not find any sources of parasitic draws, consider alternator issues next. Signs to look for include:
- A screeching or grinding sound occurs when the engine is running.
- Flickering headlights or multiple electrical issues, like slow power windows or malfunctioning power door locks.
- Over 100,000 miles on your vehicle, which could indicate the alternator is nearing the end of its life.
Fixes for Common Battery Drain Problems
How to fix battery-drain issues depends on the cause. For parasitic draws, replace any malfunctioning aftermarket parts and re-wire any accessories connected directly to battery power. “Remove the component from the constant battery source and provide it with a proper keyed ignition or accessory circuit so that it no longer drains the battery when the vehicle is parked,” Dugan says.
Replace a defective alternator if this is deemed the source of battery drain.
FAQ
How long should a car battery last?
Car batteries can last three to seven years, depending on your driving habits and climate.
Can short drives drain a car battery?
Yes, frequent, short drives can drain a car battery and shorten its life span.
About the Experts
- Justin Dugan is a car expert and brand ambassador at American Muscle, an aftermarket parts provider for performance vehicles.
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