How To Charge A Car Battery At Home (The Basics)
A quick start guide to charging your car battery:
- Observe safety precautions (covered later in this guide).
- Switch off the car engine and remove the battery.
- Find a well ventillated area.
- Attach the battery charger cables to your car battery terminals (Positive (+) to Positive first then Negative (-) to Negative second).
- Switch on your car battery charger and dial in the correct settings.
- Leave your battery to charge for the recommended time.
The rest of this instructional guide will look at the above steps in more detail.
If you have left your car headlights on or just haven’t used your car for a while, you probably have a flat car battery. The best way to deal with a this is to use a dedicated car battery charger.
Before you can learn how to charge a car battery, you are first going to need a specialized car battery charger. If you already own one, you can skip ahead, otherwise I can make a few suggestions.
Below is the battery charger that I use. It is not the most expensive battery charger, but it’s perfect for what I need, and it has some added features such as battery maintenance and recovery. There are other more expensive chargers with even more features which you may find useful.
If you are really stuck on which charger to buy, I have done some research for you and checked out what the experts are saying in our Best Car Battery Chargers buying guide. I have looked at the results that people are getting and I have tested some of them myself.
NOCO GENIUS5, 5-Amp Fully-Automatic Smart Charger
Before I show you how to charge a car battery, you will need to remove the battery from your car. Our How To Change A Car Battery guide will give you a complete set of step-by-step instructions to remove a car battery and replace a car battery.
Removing the battery before charging it is not essential if you have a garage but I prefer to remove it first for added safety.
What we will cover in this guide is listed below:
Car Battery Safety
Finding out how to charge a car battery is quite simple, but learning how to charge a car battery safely is crutial.
When working with any type of electricity, safety is of paramount importance, and car batteries are no different.
I will assume that you will be working with a lead-acid type of car battery, which you will find in most cars. Although there are some battery type variations, most car batteries have the same risks involved and will contain similar chemicals.
Car batteries will generally contain some kind of chemical, usually sulphuric acid, and when under charge, may release gasses that are flammable and can be highly explosive when mixed with the air.
When learning how to charge a car battery, you will definitely want to limit the risks of a battery explosion, and should therefore always charge them in a well ventilated area. Sparking from battery terminals could potentially ignite any gasses that have been able to build up in more confined, unventilated spaces.
Car batteries also carry a risk of electrical shock. Most car batteries will be either 12 volts or 24 volts. Although this voltage is unlikely to cause any serious harm, there are plenty of amps in a car battery just waiting to jump out through a spark.
Without a long explanation about volts and amps, you just need to remember that amps can pack a big punch, be quite dangerous and can even kill.
When working on car batteries or any electricity, it is advisable to remove all metal jewelry. Metal is conductive and can cause arcing (sparking), which can lead to electrical shocks and burns.
When connecting a battery to a charger, it is good practice to wear heatproof gloves and goggles to protect from burns and in the unlikely event of an explosion, to protect your eyes from flying debris and chemicals or acids.
Why Should You Use A Specialized Car Battery Charger
When a car battery becomes flat, many people think it is best to jump start their car and drive it for several miles to charge their battery. So why should you use a specialized car battery charger?
When flat, charging the battery by driving your car is a great quick fix, and if you do not have a dedicated car battery charger, then you have no other choice. The downside of charging your car battery in this way is that you are relying on the alternator in your car to provide enough power.
A cars alternator is designed to output just enough power to run your car and some electricals in your car whilst also keeping the battery topped up.
If you are driving with lights on, air conditioning, radio etc, the alternator will struggle so the battery will take over to provide the extra power needed. To charge a battery fully from flat, would take an enormous amount of time, and will put the alternator under even more strain.
The alternator would need to constantly work at full power, trying to run the car, electrics and charge the battery all at the same time, until the battery reaches its full charge. If you regularly let your alternator work this hard you may drastically shorten its lifespan.
The correct way to charge a flat car battery is to get it home and use a dedicated car battery charger. You will be able to charge your battery overnight, to its full capacity.
A specialized car battery charger is designed precisely for this job and will give the best results. Specialized car battery chargers may also have a built-in gauge, which can tell you how much charge your battery is getting, and this can help you to ascertain if your battery may be faulty.
Understanding Your Car Battery Charger
Before you learn how to charge a car battery, you should make sure you have read the instruction manual that came with your battery charger.
All car battery chargers operate slightly differently and Some will only be suitable for a 12 volt battery, when others may be suitable for both 12 volts and 24volt batteries. It is essential to understand how your charger works for even greater safety.
Some car battery charges will come with extra features that may help you when diagnosing battery faults.
Remember, you should never connect or disconnect your battery unless the charger is switched off.
All of the above advice should be within your battery charger manual. If you do not have a manual, a quick search online for the make and model of your battery charger should be enough to find a downloadable version.
How To Charge A Car Battery
Assuming that you have read and understand the safety aspects of working with car batteries, I can explain how to charge a car battery at home.
It is fine to charge your battery while it is still in your car, although, as vehicles are made primarily of metal, I don’t feel comfortable leaving my charger connected in this way, either overnight or when I am absent. If a charger clamp were to pop off the battery terminal, there may be contact with the car’s bodywork, creating a spark or a short through the car’s electrical system.
In my opinion, the best way to charge a car battery is to remove it first. Whether you leave the battery in your car or not is your choice.
At this stage, you should have already disconnected all cables from the battery termonals. If you have not, please read our How To Change A Car Battery guide.
Wipe away any grease or debris from the battery terminals as these may inhibit charging. A strong bristled or wire brush can be used to remove any corrosion.
Now follow the steps below:
- Make sure your battery charger is switched off.
- First connect the red (+) Positive clamp from the charger onto the positive terminal of your battery. Secondly, connect the black (-) negative clamp to the negative terminal on your battery.
- Make sure your charger has been set to the correct output, 12V or 24V, and charging time.
- Switch on the battery charger.
That’s it! You can now leave your battery to charge for the desired time.
Your battery charger may turn off automatically or you might have to turn it off yourself. You should find this information in the battery charger manual.
- Once your car battery has finished charging, you will need to switch off your battery charger.
- Remove the clamps from the battery, black (-) negative first, and then red (+) positive.
- Put the battery back into your car.
- Reconnect your car battery.
You should now have a fully charged car battery! The whole process is quite simple really and after doing this a couple of times, it should become second nature.
What If My Car Battery Won’t Hold Charge
If you have been through the steps above and you find that your car battery won’t hold charge, your battery is probably damaged and will possibly need replacing or reconditioning.
Most car batteries used today are sealed units, although some may be unsealed and have a pop-off panel along the top, which will allow you to check the electrolyte levels and top them up with distilled water. If the levels are low, this will cause poor charging performance.
If your battery still does not hold a charge, then consider replacing it or reconditioning it.
How To Recondition A Car Battery
If learning how to charge a car battery has not been successful, you may be delighted to find out that car batteries and many other batteries can be reconditioned even when you think they are ready to go out with the trash.
I was amazed to find out that you can add years to the lifespan of many batteries through a simple reconditioning process.
I found this out through the EZ Battery Reconditioning System and have had much success with several car batteries, my phone battery, and my wife’s laptop battery. Below is a short video about this system.