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Can You Leave a Car Battery Charger On Overnight? Is It Risky?


You must have heard that leaving the car battery on charge overnight affects the battery life. But that’s a misconception because it depends on the type of charging. However, it’s better to know can you leave a car battery charger on overnight for different types of charging.

There is no exact answer to this question because that totally depends on the type of charger you are using to charge your car battery. There’s nothing to worry about if you are using a trickle charger that gives low amperage. But if you are using a 12+ volts charger, there’s a high chance that the car battery will overcharge.

Therefore, let’s discuss how risky it is to leave a car battery charger on overnight. Plus, what type of car battery chargers are suitable for that.

Leaving a Car Battery Charger On Overnight

No doubt, you can leave your car battery charger on during the whole night. But before doing that, you have to make sure the charger has the smart feature installed. That feature automatically shuts down the charging once the car battery reaches its optimum charge.

Man working on car removing battery for charging

In addition to that, the charger should slowly charge the car battery. That will avoid overheating the car battery.

While charging a car battery, leaving the charger on for more than 24 hours is not recommended. Even if it’s a smart charger, such a long duration might affect the charger’s life.

Moreover, you can easily find automatic chargers as they are available in almost every automobile shop. You can go for the NOCO GENIUS10 Fully-Automatic Smart Charger. It uses trickle charging and also maintains your car battery.

On the other hand, manual car battery chargers are still widely used because of a lack of awareness. One of the biggest disadvantages of charging the car battery using a manual charger is you have to keep an eye on the charging status.

If you leave the car battery connected to a manual charger, it’s a risk. How?

Manual Battery Charger

When you leave your car battery on a manual charger, it won’t stop charging even when the battery is fully charged. As a result, the car battery gets overcharged.

Overcharging makes the car battery extremely hot, which is not a good sign. When the car battery is overcharged, the electrolytes begin to boil inside the battery.

If you don’t disconnect the charger or power it off, the boiling will continue until the electrolytes begin to evaporate out of the battery’s acidic solution. As a result, corrosion will take place on the lead plates, affecting the battery’s life.

Overcharging a Car Battery

Not only a car battery, overcharging any battery is not a good practice. Apparently, you might not see any disadvantage of overcharging. But deep inside, charging more than necessary damages the battery.

For instance, if a car battery reaches 15.9 volts, it’s considered to be sulfated or permanently damaged. That means the car battery can no longer hold the electric charge, and thus, none of the car’s electronic and electrical components will receive energy.

However, you can revive a sulfated battery if it’s in a mechanically sound condition. What does that mean?

Revive a Sulfated Car Battery

Usually, cars and other vehicles contain a lead-acid battery. Every lead-acid battery has the same functioning. Therefore, they also get affected by similar conditions.

Do you know what is the most common type of battery degradation? That’s Sulfation!

In simple words, sulfation happens when lead plates develop sulfates on their surface. Most of the time, it happens due to overcharging a battery.

Now, if you think that your car battery is sulfated, but it was working fine back then, you can revive it by following these steps:

  1. Connect the sulfated battery to a trickle or smart charger.
  2. Put it on a continuous charge for 7-10 days. The slow charging rate will gradually eradicate sulfation.
  3. Connect a wire to a battery desulfator, which desulfates the solution inside the battery. Besides, battery desulfators are easily available in the market.
  4. You might have to add a desulfator chemical (a non-acid chemical) in the respective slots on the sulfated battery. That chemical will dissolve the sulfate crystals, which causes the corrosion.

Before performing the method to revive a sulfated car battery, make sure you take the following safety precautions:

  • Wear goggles to protect your eyes from sudden eruption of steam and spark.
  • Put on rubber gloves before working with the lead-acid batteries.
  • Make sure the battery is in working condition. Sometimes overcharging deposits sulfates on the batter, which is an exception.
  • Look for damages or leakages in your battery, if any.

Now, once you have revived the car battery, connect it to that charger. But how will you know that your car battery is charging?

How to Check if the Car Battery is Charging?

The simplest way is to see the battery’s charging status light on the charger’s ammeter. If it’s illuminated, that means that the charger is properly charging the battery.

However, if there’s no charging status light, there’s a problem with either the charger or the battery. In that case, the best thing is to bring the battery and the charger to an automobile expert. They’ll identify the problem and will let you know.

charing car battery by charger

Besides, you should know that your car battery loses its power over time. So even if there’s no fault in the battery, the process of discharging and charging affects the battery cells.

Moreover, that process causes chemical reactions inside the battery.

When you normally use car electrical accessories, those reactions take place at a normal rate. That means the load on the battery is normal.

But when you turn on multiple accessories like the stereo, headlights, and interior lights, there will be faster chemical reactions. Thus, the faster the rate of the chemical reaction is, the faster the battery will reach its life expectancy.

Therefore, we’d recommend not to go for unnecessary features of your car that consume electricity. Instead, you should think about preserving the life of your car battery.

Final Thoughts

Leaving your car battery charger on overnight can cause overcharging. But that only happens when you are using a manual charger. When you use an automatic or smart charger to charge your car battery, you can leave the charger on overnight without any worry.

The automatic or smart car battery chargers are affordable as well. Therefore, get a smart charger for your car battery and save the battery from overcharging.

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