If the car battery suddenly dies on you, one of the first questions you’ll ask yourself is can you charge a battery while it’s connected to the car?
This option for solving a flat battery problem is one of the most popular. Not only for its simplicity but also for the least time needed to get out of trouble.
But as with other solutions, it would be good to know the proper and safe way to do it.
This article has the purpose of showing you that. If you don’t feel like reading you can watch the video tutorial at the end of the article or on our YouTube channel.
CAN YOU CHARGE A BATTERY WHILE IT’S CONNECTED TO THE CAR?
Before we start I would like to state as a disclaimer, that this isn’t the proper way to recharge a car battery.
The battery should be disconnected, taken out of the car, and charged for several hours. Also, it should be stored for charging in a well-ventilated room.
What we’re going to show you is a first aid measure and should be used only in case of an emergency. So, can you charge a battery while it’s connected to a car?
Yes, but under certain circumstances and you should do it only to get out of a tight spot.
Also, I would avoid this if you drive a high-tech modern car with complicated electronic systems. You never know if this might have any consequences for the car.
For more information about how to properly charge the car battery, when it’s out of the car, click here for the article and video on that topic.
1. POSITION THE BATTERY CHARGER PROPERLY
The usual scenario is: you get in the car, turn the ignition, and…..nothing. Either that or a brief click and the car is dead in the water so to say.
Well, if you’ve decided to charge the battery this way then open the hood and go get the charger.
If you don’t have an electrical socket nearby, get an extension cord also.
The first thing you should do is properly position the charger. Why is this important?
Well, know that you are putting an electric transformer, under voltage inside your engine bay.
This doesn’t sound like a good idea but the truth is if you pay attention to what you’re doing it should be OK.
Position the battery charger, if possible on a stable flat, preferably plastic surface. For instance, the engine cover (like in this example) is a good place.
The position of course depends on the engine bay and where the battery is positioned.
So, the most important thing is to put the charger in a safe, dry, and stable place so it doesn’t accidentally fall down and cause a short circuit.
Another option is to use a chair or stool for instance and put it next to the engine bay. This way it’s much safer from falling and causing an accident.
If you’re using an extension cord, it’s preferable that the connection between the charger and cord is outside of the engine bay, just in case.
2. CONNECT THE BATTERY CHARGER
Once you’ve properly positioned the charger, connect it to the battery terminals.
On the charger, you’ll usually find three cables, one for the power supply and two clamps for the battery.
Regarding the clamps, they usually have red and black (or blue) markings so you can recognize plus and minus and which goes where on the battery.
On the car battery, you’ll find similar markings. You’ll see a red cable going to plus (+) and a black cable going to minus (-). Also, you have imprinted icons on the battery, near the terminals, for plus and minus.
One rule to obey here: red to red and black to black. Plus on plus, minus on minus. Red clamp from the charger to the plus terminal on the battery. Black clamp on the charger to the minus terminal on the battery.
Simple as that. Pay some attention to doing this as if you switch them there is a good possibility that you can damage the car’s electrics and electronics. Also, the fuse on the charger may blow.
If possible put the plus first and minus clamp second.
Make sure that the charger clamps are snug on the battery terminals. If not the charging will be weaker not to mention they can accidentally snap off while under voltage.
Besides this, position them so there’s no danger of accidentally touching other parts of the car (especially the plus clamp) or touching each other.
So, connect correctly and make sure the charger clamps are tight and properly positioned.
3. TURN THE BATTERY CHARGER ON
Now that everything is connected, turn on the charger.
Most chargers have a switch but some, like in this case, are meant to be plugged directly into the socket.
Again, it would be best that the connection from the charger to the power source is outside the engine bay. If you’re using a wall socket directly, then this will be by default. If you’re using an extension cord, then try putting the reel or socket outside the engine bay.
Once the charging is finished, remove the battery charger in reverse order:
- Unplug the charger from the power supply
- Disconnect the charger from the battery (minus first then plus)
- Remove the battery charger from the engine bay. If you’ve used an extension cord, remove it also.
Needless to mention: DON’T TRY TO START THE CAR WHEN THE CHARGER IS CONNECTED!!!
First, disconnect the charger and remove it from the engine bay and then try to start the car.
Besides this, avoid leaving the charger connected too long. If you conclude that the battery needs a longer time to charge, best take it out of the car.
I must mention a very good and viable alternative for all of this.
That is the modern car battery jump starter. It’s small in size but has a very good power output. If you’re car’s engine starts without any problems and a flat battery is the only obstacle, then it should help, perhaps with less effort.
SHOULD YOU DISCONNECT THE BATTERY BEFORE CONNECTING THE CHARGER?
This question perhaps causes the most dilemma when talking about can you charge a battery while it’s connected to the car.
The brief answer to this question would be yes. If you have the time and means disconnect the battery.
By disconnecting the minus battery terminal, the car and its electric and electronic installation are pretty much safe from any problem.
So why don’t people do it, in most cases? Why isn’t the battery disconnected in this example?
Well, the true answer is because, usually, this way it’s much easier and takes less time.
You don’t need any tools, you don’t have to remove the battery clamp, and most importantly you don’t have to cut the electric power of the car.
Taking off the battery clamp means things like losing the radio code, you have to set the clock again and other various settings may be lost. Some of them might be very important not to mention complicated to return back.
So, there is much less inconvenience this way in terms of spent time, having to use tools, getting dirty, losing various settings on your car, and else.
To be honest, I’ve recharged the car battery numerous times with the battery clamps connected and there was no problem whatsoever. These were not high-end cars, mostly they were from the mid-2000-2008 range.
Again, I would not recommend doing this on very modern cars that are crammed with modern electronic systems.
HOW LONG DOES IT TAKE TO CHARGE THE BATTERY WHILE IT’S CONNECTED TO THE CAR?
This depends on a couple of factors: what kind of charger you have, what is the condition of the battery, and what kind of engine you have.
If you have a stronger charger, with more amps, it can give a boost to the battery in a matter of half an hour, or even less.
With a classic battery charger, it may take an hour, more likely two.
When the battery is still in good shape but has been depleted (like when the lights are accidentally left on) it takes much less time to revive it. But when the battery is on its last legs, it’s going to take a couple of hours or it won’t even work at all.
Know that the outside temperature is also a big factor. Cold temperatures mean more charging and time while in warmer weather it takes much less.
To simplify a bit: if you drive a gasoline (petrol) car with a battery that still works to some extent and the engine starts properly, half an hour should be enough. If it’s colder, leave it for an hour if you can.
If you drive a diesel, leave it at least for two hours provided that the battery can still charge and that the engine can start at the turn of the key. In cold weather, it usually takes a lot longer. The longer you charge, the better the chances are that you’ll start the car.
So, can you charge a battery while it’s connected to the car? Yes, you can but you have to be a bit careful.
Watch where you put the charger, how you connect it and where you’ve put the power supply.
Don’t hurry when doing this. Even if you’re in a tight spot regarding time, take it easy and think about what you’re doing otherwise you may cause even more problems.
With some luck, you may get your car running again in about half an hour or an hour.
Also, if the car battery left you down numerous times, in the recent past, best buy a new one as soon as possible. If it let you down once, there’s a good chance it will happen again in the near future.
It would also be good but not necessary, if you have the means to check the alternator voltage once you’ve started the car, just to be sure that the battery was the problem.
In the end, please remember, once more, that this method is for getting out of trouble but not for finally solving the problem.
Written by: Sibin Spasojevic
Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com
CAN YOU CHARGE A BATTERY WHILE IT’S CONNECTED TO THE CAR? YOUTUBE VIDEO