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What Drains a Car Battery? 8 Electrifying Reasons

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Waiting for roadside assistance to jump-start your car? 
Unexpected battery problems are a surprise that no one looks forward to. 

That’s why understanding why your car battery keeps dying and how to prevent a battery drain is crucial for staying ahead of battery issues. 

To help prepare you, we’ll break down what drains a car battery and the signs your car will give when running on a failing battery. We’ll also list some precautions you can take to ensure your battery issues don’t leave you stranded again. 

Let’s begin!

This Article Contains:

What Drains a Car Battery?

There are countless reasons for waking up to a drained battery. 
Here are a few common car battery drain culprits:

1. Defective Alternator  

If you have a faulty alternator or bad alternator diodes, you’ll experience charging system problems. Consequently, your car will use more battery charge than the charging system can replenish, leading to your vehicle’s battery draining completely.

A bad alternator belt could also be the case here. If the alternator is working fine, but the belt isn’t spinning fast enough, the alternator won’t charge. 

Note: Defective alternator issues are common in pre-owned vehicles.

2. Leaving Headlights On

Do you often forget to turn off your headlights?
No wonder your car battery keeps dying!

Headlights draw a lot of battery power, but this usually doesn’t lead to charging system problems. The alternator generates enough power to replenish the battery charge. 

However, if other components also draw excessive power or you have a faulty charging system, you’ll likely start experiencing issues. 

3. Parasitic Drain 

“Parasitic drain” refers to numerous components in your car continually drawing battery power even with your car turned off. 

From dashboard lights to car door sensors and air conditioning, if something is left on overnight or isn’t turning off automatically, it can cause excessive drain.

4. Old Car Battery

Old car batteries often experience sulfation, a buildup of sulfate crystals in the lead battery plates. This prevents them from properly absorbing or dispersing current. 

Sulfated battery plates won’t carry an electrical charge very well, leaving you with a weak battery that dies in a shorter period of time — a common occurrence at the end of a battery’s lifespan.

Note: Old batteries are common in pre-owned vehicles. It’s always a good idea to get a new battery when you buy one.

5. Loose or Corroded Battery Cables

Bad battery cables that have corroded will struggle to carry a charge.

Similarly, when there’s a poor battery connection between the cables and a battery terminal, the circuit between your battery and electrical components will be “open,” preventing the flow of electricity.

Poor battery connections can also occur if you have recently modified your car or replaced your car battery.

6. Frequent Short Trips

When your car starts, the starter motor uses a massive jolt of energy from your battery to crank the engine. You need to drive for the alternator to recharge the drained battery. 

However, if you only take a short drive, your vehicle’s battery won’t have a sufficient amount of time to fully recharge and will drain soon after. Avoid frequent short trips under 15 minutes, and limit the number of short drives to maintain a charged battery.

7. Car Modifications 

New electrical modifications (such as audio systems) could draw more power from your car’s battery than it can provide. When energy demand exceeds supply, a weak battery will drain completely. 

Recharging your battery is a temporary solution — a fully charged battery won’t last long if the energy demand stays high. So, ensure your battery is rated for modifications to avoid excessive drain.

8. Extreme Temperatures   

Extreme temperatures (hot or cold weather) can alter the chemical reactions in a car battery, affecting its ability to produce a charge.

Some newer batteries with a cold cranking amp measurement of over 750 amps are built to handle extreme weather and have longer battery life. While these batteries are effective, they may still go bad if you expose them to an extreme temperature for too long. 

Now that you know why a car battery keeps dying, let’s review some common symptoms of an old battery.

6 Evident Signs of a Dying Battery

If the source of your battery problem is the battery itself, you’ll likely notice some of the following symptoms:

1. Slow Crank

When the engine struggles to turn over due to a weak battery, you’ll notice shaking or strong vibrations inside the car. You may also hear a whining or clicking sound from the car’s starter motor.

2. Dim Headlights

Headlights draw significant power from the battery. A dim headlight indicates insufficient power from your car battery to go around.

3. Problems with the Electrical System

Besides the headlight, other electrical components like the dashboard lights, radio presets, or the interior light may not function correctly. These are telltale signs that your car battery isn’t keeping up with your car’s electrical system energy demand.

An electrical problem can be as simple as poor battery connections or a dome light that doesn’t turn off — draining your battery overnight.

An illuminated check engine light can also indicate battery failure. Never ignore a check engine warning.

4. Swollen Battery

A swollen battery case means the chemical buildup of a battery is compromised. This sacrifices its ability to produce and emit charge, making it unstable. When that happens, battery failure is on the way, and you must replace the bad battery. 

5. Check the “Lower & Upper” Marker

Some new vehicle batteries have an “upper and lower” marker on the side of the case that indicates its charge capacity. If the marker is low, the battery is low on charge.

6. Backfiring

A failing car battery may cause the spark plugs to fire intermittently, leading to fuel building up in the engine cylinders. When ignited, this fuel expels an increased force, causing an exhaust backfire. 

Keep in mind that a backfire could also indicate other engine issues. A proper diagnosis is required to rule out any engine repair. 

That said, there are certain preventive steps you could take to extend your battery’s lifespan and avoid a premature trip to a vehicle service center.

How Do You Prevent Battery Drain?

There are several things you can do to prevent battery drain, including:

Tip: Use a trickle battery charger if you plan on leaving a battery disconnected for long periods. A trickle charger recharges a battery at the same rate it naturally loses power. This means your battery will stay healthy for months when unattended.

Still want to know more about your car battery? 
Let’s answer some car battery-related questions. 

5 Battery-Related FAQs

Here are answers to some common questions about car batteries:

1. How to Diagnose a Dying Car Battery?

Diagnosing a battery problem or a faulty charging system is simple but dangerous if not executed correctly. It’s best to get a qualified mechanic for the inspection. They would:

  1. Use a multimeter to measure the car battery’s current voltage. If there’s no battery voltage drop, there may be a problem with the battery cable.
  1. Check the fuses for parasitic drain by noting any weak readings on the multimeter and locate the responsible electrical component (e.g., faulty interior light fuse). They’ll unplug each fuse one by one while watching the multimeter readings. If there’s a significant voltage drop on the multimeter when removing a fuse, the associated electrical component is causing the dead battery. 
  1. Test the alternator’s charge —  if the battery and fuses work fine, a faulty alternator is most likely the culprit. A bad alternator won’t provide any charge readings on the multimeter.   

2. Can You Repair a Car Battery at Home?

Absolutely not!

Attempting to repair a dead car battery or damaged battery terminal at home can expose you to dangerous chemicals — leading to severe burns and injury. It’s best to get a new battery if you notice failing battery symptoms.

However, battery corrosion is the exception for home repair. Corrosion can be fixed with a light scrub with a steel brush. Remember to disconnect the battery first when tackling corrosion.

Tip: If the battery isn’t damaged, only dead, try using a battery charger to revive it. 

3. Does Jump-Starting Another Car Drain a Battery?

Yes, jump-starting another car draws significant power from your battery. 
This power drain is usually recharged through the alternator during driving. However, the battery may require an additional charge to recover fully. 

Don’t have jumper cables?
No problem! Learn to jump-start a dead battery without jumper cables.

4. What’s the Difference Between Standard and Premium Car Batteries?

The two common types of car batteries are:

The difference is in the needs of the car. Premium batteries tend to hold more charge and have longer battery life. While premium batteries are common in new vehicle models, the traditional lead acid battery is still used in most cars on the road today.

It’s best to know your car’s energy requirements before you schedule service for a new inventory — you don’t want to order parts that don’t work with your car.

5. How Much Does It Cost to Fix a Dead Car Battery Issue? 

Typically, a new inventory for car battery replacement will cost between $79-$450, depending on the vehicle and battery type. 

A modern vehicle will often incur a higher car battery replacement cost as the batteries are more expensive. However, these newer batteries tend to last much longer than an old battery model. 

For reference, here are some cost estimates for repairs (including labor):

Note: While your warranty may cover a battery replacement, coverage varies for different parts and procedures. For example, services like tire rotation need to meet specific criteria for the tire warranty to cover them. Likewise, it’s essential that you’re aware of your battery service warranty options before you order parts for replacement.

Resolve Your Battery Troubles with AutoNation Mobile Service

A dead battery is a sure way to cloud your day — no one enjoys unexpectedly having to wait for roadside assistance. 

If your car battery keeps dying and needs a battery replacement, contact AutoNation Mobile Service!

Rather than you going to a service center, our qualified mechanics can perform any auto repair or replacement right in your driveway. All repairs come with a 12-month, 12,000-mile warranty, exceptional customer service, and easy online booking.

For an accurate estimate and to schedule service at home, just fill out this online form.