Can You Charge A Car Battery Without Disconnecting It?

If you’re wondering whether you can charge a car battery without disconnecting it or not, then you’ve come to the right article! Not only will you learn the answer to this question, but you’ll also learn the pros and cons of doing so, how to do it, precautions you’ll need to remember, and much more!

So keep reading to find out everything you need to know!

Can You Charge A Battery Without Disconnecting It?

For the most part, you can absolutely charge a battery without disconnecting it; however, it’s important to remember that you should only do so if you’re using a smart charger or trickle charger. If you’re using a regular charger, then it’s best to disconnect the battery beforehand, as they don’t have the same controls in them to regulate charging.

What Kind Of Charger Should You Use?

If you’re going to charge your battery without disconnecting it, then the type of charger you use is important as well. If you’re going to charge your battery, then you should use the following chargers:

Smart Charger

The first type of charger you should consider using is a smart charger. Smart chargers have built-in controls and regulations that ensure your battery is going to get the amps it can handle.

Smart chargers can sense when a battery has been fully charged and then switch off accordingly, making sure the battery doesn’t become overcharged.

Trickle Chargers

As well as smart chargers, you can also use trickle chargers to charge your battery without disconnecting it as well! Trickle chargers provide a minimal amount of amps to the battery. And in most cases, just like with smart chargers, when trickle chargers have charged a battery to full, they’ll switch off automatically.

However, you should be warned that in cases with older trickle chargers, this may not be the case, and you’ll have to switch the charger off manually.

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Are There Times When You Should Disconnect The Battery?

As you can probably guess by now, there are going to be times when you should disconnect your battery from the car when you plan on charging it. Here are the times when it’s best to disconnect:

When You Have An Old Charger

As you know already, you should always disconnect your battery when you have an old charger. This is because older chargers don’t have processors in them to regulate how much current is being provided, resulting in overcharging.

When The Battery Isn’t Sealed

Another time when it’s best to take the battery out is when it hasn’t been sealed. This is normally the case with older batteries but not so much with newer ones. If you do leave these batteries in when you’re charging them, it could result in the battery exploding.

When The Battery Is Dead

And lastly, you should disconnect the charger when the battery has died completely. At this point, a trickle charger isn’t going to provide enough current to overcome the internal resistance of the battery.

Why You Should Disconnect The Battery When You’re Using An Old Charger

You may be wondering why it’s so important to disconnect the battery if you’re using an older charger. Well, there are actually a number of reasons.

Of course, as you know, the biggest reason to disconnect is to avoid overcharging. This is because neither the battery nor the charger are able to sense how the amount of amperage the battery still needs, so energy will just keep getting pumped into it.

When this happens, your battery won’t have anywhere for the excess energy to go. When this happens, it begins to pass an electric current through the fluid, heating it up and causing it to boil it off. This boiling off doesn’t stop, however, and results in the battery having less charge than it did when you started charging.

As well as this, if your battery heats up too much, it can also cause the outside to begin to warp and bulge. Not only is this going to ruin the battery completely, but it also makes it more likely that the battery might explode in the future.

What Are The Benefits Of Charging A Car While It’s Connected?

So, now you know that it’s possible to charge a battery while it’s still connected to the car, you may be wondering what the benefits of doing so are. Here are the following benefits you can expect:

You Won’t Lose Any Setting

When you disconnect your battery from the car, you’ll lose the settings on the clock and radio. However, charging while the battery remains connected helps you avoid this problem.

It’s Faster

And secondly, charging your battery while the car is connected is a lot faster and easier. You’re not going to have to worry about disconnecting it and removing it or putting it back. You can just plug your charger in, connect it and let it wait!

Are There Any Downsides To Charging A Battery While Connected?

While there are some great benefits to charging a battery while it’s connected, there are also a couple of downsides as well.

You Can Only Trickle Charge

One of the biggest downsides is that you’re only going to be able to trickle charge the battery while it’s connected. Otherwise, when a charge is too high, it could result in the electronics in the car becoming damaged.

It Won’t Revive A Dead Battery

And secondly, if your battery is completely dead, then charging it while connected is not going to provide enough current to charge it. Instead, it will need to be disconnected so it can be charged with an adequate current.

How Do You Charge A Battery While It’s Connected?

Now you know that the battery can be charged while it’s connected, here’s a step-by-step guide on how to do it!

Connect The Charger To Your Battery

The first thing you’re going to need to do is to connect the charger you’re using to the battery of your car. Remember to attach the positive clamp (red) to the positive terminal and the negative clamp (black), a grounded point as far away from the battery as possible. If you’re not sure which is which, the positive will have a “+,” and the negative will have a “-.”

Set The Correct Voltage

Next up, you’re going to need to set the correct voltage on the charger itself. If you need the car in a hurry, then higher amps and voltage is better; however, if you have time to charge your car overtime, then lower amps and lower voltage are better.

As a rule of thumb 10 amps or less is a slow charge, whereas 20 amps or higher is a fast charge.

Let It Charge

Now all you need to do is plug your charger in and let your battery charge. A lot of battery chargers have built-in timers or automatic shut off times. So check the instructions of your charger to see how you’re meant to use it!


And lastly, once your battery has been charged enough, you’ll just need to disconnect it. Turn off the charger and then remove the cables. Making sure to remove the negative cable first, and then the positive cable after.

Precautions When Charging A Car Battery

When you’re charging your car battery, there are a few precautions you should take beforehand to ensure that you’re doing so safely and effectively. Here’s what you should be aware of throughout the process.

Charge In A Well-Ventilated Area

The first step is to make sure you’re charging your car’s battery in a well ventilated area. When batteries are charged they release hydrogen gas which is both flammable and toxic. In a well ventilated area, this isn’t a problem. However, if you’re charging them in a sealed room, then it could result in the gas accumulating.

Turn The Ignition Off

You should also make sure you’ve turned the cars ignition off when you’re charging as well. If you leave the car running while it’s charging, then it’s going to constantly be draining the battery, making the time it takes to charge even longer.

Connect The Cables Correctly

You should also make sure you’re charging the cables correctly as well. Remember the positive cable should be attached first, followed by the negative cable. Then when it’s time to disconnect, remove the negative cable first, and then the positive one.

Can You Start A Car While The Battery Charger Is Attached?

Yes it’s entirely possible to turn on your car while the battery is charging. However, it’s not recommended. Not only will it drain the battery faster, there’s also the risk of the wires getting caught in moving parts of the engine, which you definiltey don’t want.

Turning the battery off before you start charging is also going to reduce the chance of shocks and other accidents occurring as well.

On top of this, you may be wondering whether you can crank the engine when charging, which also isn’t recommended. Doing this, in fact, can damage your car even more.

Can You Trickle Charge A Battery Without Disconnecting It?

Just like normal charging, it’s also possible to trickle-charge your battery without disconnecting it as well! Because trickle chargers are more regulated, the chances of something going wrong are a lot slimmer as well!

Just remember, that even if you’re using a trickle charger, once your battery is fully charged, you should remove it.

How To Trickle Charge A Battery

If you’re wondering how to trickle charge your battery while its connected, it’s similar to using a normal charger! You just need to:

  1. Set the charger to the correct voltage, this may be different depending on the brand of charger you’re using so you should always read the instructions beforehand.
  2. Then attach the clamps, positive first, and then negative after (to a grounded point).
  3. Then just turn on the charger and let the charging begin. Trickle chargers tend to charge at a lower amperage so the process may take longer.


Here are some frequently asked questions that people have when it comes to charging their car!

How Long Does It Take To Charge A Battery

How long it takes depends entirely on the type of battery you’re using, and how charged the battery is. For example a trickle charger may take up to 2 days to charge a dead battery. However, if the amperage and charge in the battery is higher, it will be quicker.

Is It Safe To Charge A Battery Overnight Without Disconnecting It?

If you’re using a trickle or smart charger then it’s safe to charge the battery overnight without disconnecting. However, fif you’re using an older charger, you should avoid doing so. Trickle chargers and smart chargers will turn off once the battery is fully charged. However, older chargers may not.

What Happens If You Leave A Car Battery Charger On For Too Long?

If you leave a smart charger/trickle charger on for too long, then it will go into float mode and turn itself off, so you don’t have to worry about the battery being damaged. However, if you’re using an older charger, then it’s not going to know when the battery is overcharging, so you may end up damaging it.


Now you know it’s perfectly fine to charge your car battery while it’s connected, just make sure you’re using a smart or trickle charger. The only times you should disconnect the battery is when it’s dead, it isn’t sealed, or you have an old charger.

If you liked this article, make sure you check out the rest of the website! Otherwise, have a great day!

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