Is Your Starter Secretly Draining Your Car Battery? (5 Steps to Diagnose)

Often discussed, can a faulty starter drain your car’s battery? The short answer is yes, it can. Under certain conditions, a malfunctioning starter may deplete your vehicle’s battery.

However, this issue is more complex than it appears on the surface. Read on to learn more about starters, and the potential of unwanted amperage draw.

testing voltage with multimeter

How a Bad Starter Can Drain a Car Battery

A bad starter can drain a car’s battery through an electrical condition known as a parasitic draw. Parasitic draw is defined as an unanticipated discharge of electrical current, to a device or component that is not in use, primarily when a vehicle’s ignition is in the “off” position.

This draw, including its severity, can be measured in amperage. If significant enough, or sustained for a long enough period of time, parasitic draw can fully discharge a vehicle’s battery.

A vehicle’s starter is best characterized as an electrical motor. When powered, a unitized external power contact, known as a solenoid, allows the energization of additional contacts on the starter motor itself, thereby allowing its engagement. In the event of a starter-related parasitic draw, partially stuck/welded internal contacts, failed windings, or an internally shorted solenoid are often to blame.

How Quickly Can a Faulty Starter Drain a Battery?

The rate at which a bad starter can potentially drain a battery differs by exactly how much amperage is being drawn by the starter in question. The higher the amp draw, the faster a vehicle’s battery will be discharged. This factor also tends to be the underlying factor in determining just how noticeable this draw is.

In some cases, starter-related amp draw might take as long as a couple of days to completely drain a vehicle’s battery. In more severe cases, a battery can be drained almost entirely after sitting overnight. These are the parasitic draws that do not go overlooked for long.

Symptoms of a Starter-Related Battery Drain

bad starter symptoms

Starter-related battery drain is often accompanied by a host of underlying symptoms, many of which tend to be relatively inconvenient to deal with. Spotting these symptoms early can help you avoid bigger issues and get your car fixed quickly.

Here are several of the most common symptoms associated with starter-related battery drain.

See Also: 4 Reasons Your Starter Spins But Doesn’t Engage

If Not the Starter, What’s the Problem?

There are a number of additional electrical system issues that can lead to a notable battery drain or parasitic draw. In many cases, a vehicle’s starter will not be the actual cause. In these cases, it’s vital to identify the source of the unidentified draw as soon as possible.

The following are the most likely culprits of parasitic draw, in instances where a vehicle’s starter is not to blame.

  • Defective alternator diodes
  • Internally failed electrical accessories (stereos, clocks, etc.)
  • Lights left on after shutdown

Diagnosing the Battery Drain

testing relay with multimeter

The following steps can be used to assist in diagnosing the source of your vehicle’s parasitic draw. It is also advisable to obtain a manufacturer-specific service manual for your particular model of vehicle before delving into such efforts.

#1 – Hook Up Multimeter In Series

Begin by disconnecting your vehicle’s negative battery lead. Then, using a multimeter capable of reading amperage, hook both test probes in series between the vehicle’s negative battery post and negative battery lead. Testing is most often conducted on the mA scale.

#2 – Let All Modules Time Out

Next, allow all of a vehicle’s intelligent modules to time out and de-energize. This process typically takes 20-30 minutes. During this time, all vehicle doors should be shut, and all lights should be disabled.

#3 – Read Amp Draw

After all modules have timed out, read the amp draw shown, with your multimeter prepared as described above. These readings should be compared to permissible values specified by your vehicle’s manufacturer. If these readings exceed permissible values, further troubleshooting will be required.

#4 – Begin Isolating Circuits

With a true parasitic draw identified, it will be necessary to locate its source. This is most easily done by removing a vehicle’s fuses from the under-hood fuse box, one-by-one. While removing these fuses, look for a noticeable drop in amp draw.

Any affected circuits that are identified should receive further troubleshooting. It is also necessary to perform the same testing on any circuits pertaining to in-cabin fuse boxes, if so equipped.

#5 – Assess Larger Electrical Components

If testing during step #4 did not reveal any noticeable drop in power discharge, it will be necessary to further assess your vehicle’s starter and charging system components. A vehicle’s alternator can be easily checked for draw by unplugging or disconnecting its power/ground leads while looking for a noticeable reduction in draw via your multimeter.

If no changes are observed, an amp clamp should be used to measure amp draw across all wires and cables associated with the starter. Any noticeable draw detected while sitting idle would be indicative of a faulty starter/starter solenoid.

Does Modern Start-Stop Technology Play a Role?

automatic start stop technology

People often wonder how hard modern start/stop technology is on a car’s battery and starter. While it is undeniable that this feature places additional strain on a vehicle’s starter, most vehicles are equipped with re-engineered starters of increased durability.

Likewise, vehicles utilizing this technology are outfitted with specialty AGM start/stop-rated batteries, designed to withstand frequent yet brief occurrences of higher amp draw.

In short, thanks to these engineering improvements, premature starting and charging problems are less likely than some people fear. While still possible, they’re not a major concern.

Most starter or battery issues in these vehicles are likely due to normal wear and tear on aging parts, rather than the start/stop technology itself.

Josh Boyd

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