Can A Starter Drain A Battery Overnight – [Detailed Guide]

Yes, a faulty starter can completely drain a battery overnight. However, keep in mind that the starter is only one of several factors that could cause your battery to discharge overnight. 

I’ll go over the five main reasons batteries drain, how to tell if your battery is draining, and how the starter and battery work together on a car in this blog post. I will also share a few expert tips on how to care for your car batteries. 

Let’s first understand how a car battery functions. 

TLDR; How does a car battery start a car?

Here’s how a car battery and starter work in a nutshell: when you enter your car and turn the keys, or push the ON button in modern vehicles, a signal is sent directly to the battery.

The signal tells the battery to do a chemical reaction with its components and convert chemical energy to electrical energy. Once that’s done, the electrical power is forwarded to the starter to crank the engine and power the vehicle. 

You can watch this video to see what chemicals are inside a car battery and how the chemical reaction takes place. 

How Can A Starter Drain A Battery Overnight: The Solenoid

The main culprit behind your car’s battery draining overnight is the solenoid. 

The solenoid, also known as the starter relay, sits in the middle of the ignition module and the engine. The electrical power supplied from the battery passes through the solenoid and reaches the engine. Then, the engine uses the received electrical power to keep the car turned on. 

If there are any malfunctions, or if the solenoid fails to send the required electrical power to the engine, the battery will be damaged in turn. In most cases, though, the starter relays, also known as solenoids, fail to work when they are worn out. 

If a person experiences any problems with the starter, it is strongly advised to consult a technician or visit a repair shop. 

How to Know if You Have a Bad Starter?

There are five ways you can confirm if your battery is out of service and needs replacement. 

Noise

One of the easiest and most certain ways to confirm that the starter is worn out is by noise. If you can hear any grinning or whirring noise from the starter when turning the keys, it’s a sign that the starter needs replacement. 

Engine Failure

Another certain way to detect a damaged starter is that it fails to do its primary job, which is to start the engine. The starter uses chemical energy from the battery to provide electrical power to the engine.

If it fails to do so after several attempts, it means the starter is gone for good. Another clear sign is that when you turn the keys or turn on the vehicle, the headlights turn on properly but the engine remains off. 

However, I should mention that there could be other reasons why your car’s engine fails to start. It would be best to visit a technician if you are not properly skilled at performing a thorough check on the car. 

Oil Leaks

An oil leak is a visual indication that the starter is damaged or worn out. Check on the starter and see how it’s doing. If you find that the starter has leaked oil and is soaked in it, you need to change it as soon as possible before it damages the battery any further. 

Smoke or Smell

Any dark smoke or unusual smell from the starter is a confirmation that the battery is out of service and needs immediate replacement. 

How can I tell if my starter is draining my battery?

If you can identify any of the above five indications of a damaged starter on your starter, there’s a high probability that your starter is draining your battery. 

In this circumstance, you can either change the starter or get a technician to confirm the exact cause of why your car battery drains overnight. 

Can the battery drain from a bad starter when the car is off?

Yes, a bad starter can cause the battery to drain even when the car is off. This happens because the starter is always attached to the battery with the cables. 

What can drain a car battery when the car is off?

There are a number of things that can drain a car battery even when the car is off. 

Parasite Draw

One of the most common reasons is parasite draw. It refers to the condition where the battery drains off each night from an unusual power discharge. You can watch this video to learn how to run a parasitic draw test and how to solve the problem. 

Electrical Items

If you mistakenly keep the headlights, indoor lights, or any other electrical items on, they can drain the car battery overnight. 

Weather

An extremely hot or cold night can also cause the battery to drain significantly. 

Battery Age

If your battery is three or more years old, it can slowly start to have less power and drain the charge overnight. You can consult a technician to check if the battery is in optimal condition or not. 

How Can You Prevent a Bad Starter From Draining Your Battery?

One of the best and most practical ways to prevent a bad starter from draining the battery is to disconnect the battery cables from the starter at night. If the starter has lost the connection to the battery, it can not suck the power out of it.

How Much Does It Cost to Replace A Starter?

A car starter can cost you anywhere between $80 and $350, depending on the car and battery model and brand. Of course, you will need to add the labor cost if you need assistance with installing the starter. 

How to know if the starter is draining the battery?

There are two ways to confirm if the starter is draining the battery: 

1. When starting the vehicle, you may notice unusual whirring or grinding sounds. This indicates that the starter has been damaged, causing the battery to suffer as well. 

2. You can use a multimeter with amperage to check if the starter is draining the battery. You can watch this video to do just that.

Summary 

A bad starter can drain the battery overnight. But a bad battery is not the only reason why batteries drain overnight. A few other factors, including weather, parasitic draw, battery age, etc., play a role in draining the battery overnight.

It’s highly recommended to get a thorough check from a technician to identify and resolve the issue with the battery.