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Can I Start A Car With A Battery Charger Connected?

Like many car owners, you may be wondering if you can start your car while it's connected to a battery charger. We're going to take a look at this question from both sides of the issue to see if you can or can't start your car with a battery charger connected.

Yes, if the battery is already fully charged and you just happen to forget to disconnect the battery charger. In this case, your car draws power from the battery and not from the battery charger.

On the other hand, if your car battery is totally drained and the battery charger is just starting to trickle charge it, then you might not have enough amperage to actually start your car.

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Keep in mind that a car battery charger is designed to charge a car battery. It's not designed to be used alongside a car battery when starting a car. However, if you're interested to know how to jumpstart a car using a car battery charger, just keep reading as we explain the whole process below.

Starting A Car While Connected To A Battery Charger

battery jumper cables connect to car battery for charging dead battery

It's not recommended to start a car while connected to the battery charger, as this isn't the device's purpose. The charger alone might not have enough amperage to start a low or completely drained car battery. 

If your car battery charger features higher amperage settings, then you might be able to get enough current to start your car. The best way to find out if your battery charger will work for you is to check the cranking amps specification on the battery. Some vehicles reportedly are able to crank at 50 amps.

However, if the charger has finished its task and your car's battery is topped up, then starting it while still connected to the charger will not pose a problem. The charged battery will start the car, without relying on the charger. 

7 Steps on How to Jumpstart a Car Using a Car Battery Charger

Knowing how to jumpstart a car battery is very important because it can get your car started on the road even when your car battery is dead.

It is commonly used when there is no power supply available in your vehicle, and this could happen to you at a time when you least expect it.

In order for the jumpstarting to be successful, you need to make sure you have higher amperage settings in your car battery charger. It may not work if it only has one amperage setting, especially if it's less than 50 amps. 

Here are the steps:

  1. Disconnect the battery from your car. You don't need to remove the battery. Just disconnect the battery cables.
  2. Hook the car battery charger's cables up to the battery terminals. Red goes to the positive terminal; black goes to the negative terminal.
  3. You can only hook the black to the negative terminal if the battery is not completely dead. If the battery is dead, then don't hook it up. Otherwise, you run the risk of a possible explosion.
  4. Plug the car battery charger into a power outlet. You may need an extension cord for this.
  5. Set the battery charger to 10 amps for a couple of minutes.
  6. Switch to 50 amps charge and go ahead and start the car. Do not let it stay at 50 amps for too long; otherwise, you risk frying your battery. Rush immediately to the driver's seat and start the ignition right after switching it to 50 amps.
  7. Once the engine turns over, set the battery charger to a lower amperage setting immediately and unplug it from the power outlet.
  8. Disconnect the cables from the battery terminal.

How to Test If a Car Battery is Good or Bad [5 Steps]

  1. Get a multimeter and set it to the "DC voltage" setting. Make sure the car engine is off before you proceed to the next step.
  2. Connect the red probe to the positive battery terminal and the black probe to the negative terminal. The positive terminal has a (+) sign in it; the negative terminal has a (-) in it. A good battery should give you a voltage of 12.6 V when the engine is off. If it's below 12 V, then you may have some issues with the battery. 
  3. Try starting the engine and observe how much voltage drops the battery shows. Normally, the voltage will drop down to 11 V when the car is started.
  4. This is because the starter motor is drawing a huge amount of current from the battery. If the voltage drop is lower than 10V, then you have some issues with the battery.
  5. You'll notice that the voltage will increase to up to 14V after a while once the engine is running. This is because the alternator is spinning and giving your battery some more juice.

At this point, if you notice that the voltage is not increasing, then it's either you have a problem with the alternator or the battery itself.

Testing a car's battery voltage only tells you the state of charge of the battery, which does not guarantee that the battery is in good condition.

In fact, a dead car battery can still give you a good voltage reading. In order to fully understand the overall health of your battery, you need to have it load tested.

Check out this digital multimeter on Amazon.

How to Load Test a Car Battery

  1. Disconnect the battery cables from the battery terminal. Make sure the engine is off.
  2. Connect the red clamp to the battery's positive terminal and the black clamp to the battery's negative terminal.
  3. Press and hold the test button for a minimum of 10 seconds.
  4. Release the button after 10 seconds and observe where the needle pin is pointing. You should see the needle pin move to the left or right, depending on how the load tester interprets your battery's condition.

Check out this load tester on Amazon.

Does a Car Battery Charge With Amperage or Voltage?

battery charging cables transferring power to a dead battery

Amperage, commonly known as amps, is the rate at which a battery draws electrical current. A car battery charger charges through a current flow. In terms of battery charging, car batteries are charged with amperage.

However, not all battery chargers charge at the same rate. Some charge faster, while others take longer to reach full capacity. There are also car battery chargers that offer you the choice to charge at different amperages

How Many Amps Can a Car Battery Charger Supply?

Asian young woman charging a car battery from the other car by using battery connector jump between battery, Asian young woman charging a car battery from the other car by using battery conne, Can I Start A Car With A Battery Charger Connected?ctor jump between battery

A car battery charger is generally rated in amp hours. Most car battery chargers have an amp hour rating of 48 amp hours. This means that it will give out two amps per hour of current in a 24-hour charging cycle.

You can do the math if you want to know how many amps your car battery charger can actually supply in a certain period of time. 

How Many Amps are Required to Start a Car?

A typical starter motor in a small to medium-sized car requires no more than 400 amps of current. This means that a fully charged car battery can provide enough amps for a starter motor to make the engine turn over.

Bigger vehicles, however, require much more amps. A larger car or truck might need 1,000 amps or more to start it. If in doubt, refer to your car's owner's manual for the amperage requirements.

Accumulator charging. Hands and terminals. Car repair

Can I Leave a Car Battery Charger Connected?

Car battery chargers are designed to be disconnected from the battery whenever they have achieved the desired charge. However, it is not uncommon for such chargers to remain connected to the battery for extended periods of time.

High-quality car battery chargers are equipped with safety features that prevent overcharging. However, this doesn't give you the green light to leave the charger connected to the battery for more than 24 hours.

Always be mindful to disconnect the battery charger after it has fully recharged your car battery. 

What Happens If I Leave the Car Battery Charger Connected to the Car Battery for More Than 24 Hours?

Car battery chargers are generally designed to be used for a limited time. They can be used for 24 hours if the battery is properly discharged, and they should be disconnected after that time.

If you leave the battery connected to a charger for longer than 24 hours, you risk damaging the battery itself and compromising its lifespan.

Trickle Charger Vs. Regular Battery Charger: What's the Difference?

Trickle chargers are designed to slowly charge a battery over a longer period. When you connect the trickle charger to a battery, the charger will slowly release (or trickle) a low amount of voltage into the battery.

On the other hand, regular battery chargers are designed to quickly charge a battery. When you connect a battery charger to a battery, the charger will begin releasing a steady stream of high voltage into the battery.

Maintenance check in your own car battery

Can I Start My Car While It's Connected to a Trickle Charger?

There are certain conditions that should be met first before starting a car while on a trickle charger. If you are about to start your car, you should know that you should never do it while it is charging, except when charging through the alternator.

First of all, it just doesn't make sense to have your car battery connected to an external battery charger unless you're trying to jumpstart it. This is because your car already has an alternator that will keep your battery charged as the engine runs. 

In addition, you need to have the trickle charger plugged into an outlet to get it to work. This means you'll have to eventually disconnect it when you want to start your car. You should make sure that the trickle charger has fully charged the car battery before starting it.

In Closing

Asian young woman charging a car battery from the other car by using battery connector jump between battery

To recap, you have to have an adequate amount of amperage to crank your car. If your charger has sufficient amperage, you will be able to crank your car by jumpstarting it. Make sure you've already assessed the overall condition of the car battery. 

A battery that is completely flat has a different jumpstarting approach compared to a battery that just needs a little more juice. 

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