Can a car battery recharge itself overnight?

Cars are very complicated for people who don’t know much about them. And it is not hard to assume things like a car battery recharging itself overnight. But does a car battery recharge itself overnight? Here is my answer.

Car batteries do not recharge themselves. Car batteries only recharge when you start your car, and the alternator starts to provide power to the car battery. If you have noticed that your car battery has recharged overnight, it means either your battery is dead or it needs recharging.

Car batteries consist of lead plates submerged in a fluid called an electrolyte. It uses a chemical reaction to store and provide electrical energy. Car batteries recover some electrical energy after no more drain is happening.

EXPLAINED: Why it seems that a car battery has recharged overnight?

Let me explain how the chemical process affects your car battery’s output power and why it might seem that it has recharged overnight.

You might have noticed that starting a car that doesn’t start on the first few tries will quickly reach a point where your car battery won’t even be able to turn over the engine anymore. But, if you let it sit for some time, the car battery magically appears to works again.

When cranking the engine, you are pulling large amounts of current from the battery. Since the electrical power is produced by a chemical reaction, huge current draws will cause the electrolyte on the plates to turn to water. It will slow down or even stop the chemical reactions in the battery.

When you let the car battery rest for some time, the water and gaseous deposits on the plates will get replaced by the concentrated electrolyte. It will cause the battery to magically work again.

What should I do next?

If you have noticed that your car battery has recharged itself overnight and you were able to start your car normally, then you are good to go. Just drive around the block a couple of times to recharge your battery enough so it will start your car the next time.

Optionally, you can go to your local auto parts store and get your battery checked for peace of mind. This way, you will be sure that your battery is healthy and won’t cause any unexpected problems.

But, if you are not able to start your car or the battery seems unreliable, then it’s time for a replacement.

A car battery lasts only 3-5 years and many things cause a battery to fail. Some reasons for car battery failure are:

  • Extreme cold or hot temperatures.
  • Extreme shocks or vibrations.
  • Deeply discharging the battery.
  • Poor maintenance of flooded batteries.
  • Overcharging or undercharging due to a bad alternator.
  • Battery sulfation over time.

How to tell if a car battery is dead?

Apart from losing and regaining charge unexpectedly, there are a few common signs of a dead (or dying) car battery.

1. Dim lights in the dashboard.

The battery in your car provides power to the electricals, including the lights in your dashboard. If you notice that lights are dim in your dashboard, this means that the battery is unable to provide enough power to the electrical system of your car.

You may also notice dim dome lights or no chimes when you open or close the doors of your car. In some cars with a dead battery, keyless entry will not work.

2. Not being able to start your car.

If you hear clicking noises from the starter motor or the starter motor is having a hard time turning the engine over. It means that the battery is unable to provide the high current needed for the starter motor.

In most cases, the battery needs to be recharged. But this could also mean that your battery is dead and needs replacing.

3. The car starts but stops immediately.

It means that the car battery has enough power to spin the starter motor and start your engine. But then suddenly no power is left for the ECU (electronic control unit), and the engine dies instantly.

In some cars, the clock and/or radio will reset and lose presets after you have started your car.

4. Corroded battery terminals.

Lead-acid batteries tend to release acidic gasses over time. These gasses can cause the battery terminals to corrode causing a bad connection to the car.

Usually, cleaning the terminals and rinsing them with lukewarm water fixes the battery-related issues. However, if the terminals are left uncleaned for long periods, it could end up permanently damaging the battery.

5. Swollen or misshapen battery case.

Car batteries are rectangular by design. If you notice any swelling or bulge in the battery case, immediately replace the battery.

A swollen battery is never a good sign. It might explode due to the high pressure and gaseous buildup from inside the battery.

6. Leaking acids out of the battery.

In lead-acid batteries, sulphuric acid is used as an electrolyte. It is a highly toxic acid. It is not only dangerous to human skin but causes corrosion and damage to the car.

If you have noticed some liquids leaking from your car battery, do not touch those and immediately rinse with warm water.

How often should you replace your car battery?

Service Experts and car electrical technicians recommend changing your car battery every 3 to 5 years. In the real world, car battery replacements depend on various factors, like temperature, vibrations, usage, and your make and model.

What type of car batteries are available to choose from?

There are two main types of car batteries used today: Lead-acid batteries and AGM (absorbed glass mat) batteries. AGM batteries are superior to lead-acid batteries due to their 80% DOD (depth of discharge rate), no toxic degassing, and versatility of installation options. Lead-acid batteries are cheaper, but they suffer from corroded terminals and require maintenance.

How much does a replacement car battery cost?

The average cost of a car replacement is $50 to $300. This price depends heavily on the battery technology, power capacity, engine size, cold-cranking amps, and other features. You can visit your local auto parts store or use Amazon’s Your Garage service to find a replacement battery for your specific car.

Walmart also sells budget friendly car battery. According to reviews I have read online, these batteries seem reliable and durable. Walmart batteries are manufactured by Johnson Control which makes some of the best car/vehicle batteries in the world.

Like most other auto part stores, Walmart offers free testing and recycling of your used/old car batteries.

How do protect the battery terminals from corrosion?

Using a battery terminal grease is a cheap and effective way to protect terminals from corrosion. Before applying the battery terminal grease, make sure the battery terminals and connectors are clean. You do not want any remains of corrosion on the battery connectors. Using a brush to apply battery terminal grease to exposed battery terminals and connectors is a reliable way to prevent acidic corrosion.

How to charge a car battery at home?

To recharge your car battery you will need a smart-battery charger. These types of battery chargers use a smart combination of bulk charge and trickle charge to safely charge the battery. These smart chargers are widely available on Amazon and other auto-parts stores.

Sources:
BatteryStuff
RepairSmith

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About Frank Diaz

Hi everyone, my name is Frank Diaz and I am the face behind GaragestPicks. I studied Mechanical Engineering at Georgia Institute of Technology and worked as a mechanic for over 20 years. I love working on cars and doing DIY projects around the house. I write this blog to share my knowledge and help others fix their cars with most common tools.

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