How to Charge a Car Battery

How to Charge a Car Battery. Unlike your mobile phone, there’s no ‘charge battery’ warning that flashes up on your dashboard if you’re running low on power. 

Instead of a warning, your car just won’t start. You may get a few dashboard lights to switch on – but either way, you’re not getting to work on time.

So, what do you do?

Well, if you’re reading this sitting in your car 8:30, you probably need to call a taxi and/or your boss. But, if you’re reading this with a couple of spare hours and you’re willing to get your hands dirty, we might be able to help get that car battery charged again.

Why do car batteries go flat?

You know that phrase ‘prevention’s better than the cure’? Well, that’s definitely true when it comes to a dead car battery. Roughly 90% of the time, a dead battery is a result of a driver error – and it’s usually something simple.

For instance, your battery charge will almost certainly deplete if you:

• Leave anything electrical on for a long time while the car’s not running (lights, indicators, hazard warning lights, stereo – etc)
• Use the air conditioning while the car’s not running
• Don’t maintain your battery properly
• Don’t start the car for long periods of time

Now, these aren’t the only reasons a battery might die. There are a few auto-electrical reasons too:

• A faulty or failing alternator
• A faulty electrical connection that draws power from the battery when the car isn’t in use
• If the weather is especially cold (the reduced temperature reduces current the battery can produce)

So, if you can avoid those things, you’re ahead of the game (and getting to work on time). 

How do you charge a car battery – step by step

Now to the important part – how to charge your vehicle battery if it’s just not got enough power to start your car.

At this point, it’s worth adding that every car battery is a little different – where they’re located, how to access them, how to carry out maintenance – etc. You should always start by checking your vehicle handbook and making sure you follow any vehicle-specific guidelines in there. If you can’t find your handbook, you might be able to download a digital copy from the manufacturer website.

Step 1 – Safety first

We know – we live in a world where health and safety seems to zap the fun out of everything. The thing is, there’s no fun to be had when you charge a car battery and it explodes – so in this case, you really need to take safety seriously. 

Take care to ensure you’re working in an area with no naked flames, no chances of sparks, and no smoke. Keep the area you’re working in clear of any clutter and unnecessary tools, and take off any jewellery you have on. Also, put on a pair of safety glasses and gloves before you get involved in the engine bay.

Step 2 – Do a quick battery safety check

Although it doesn’t have any external moving parts, there’s actually quite a lot that can go wrong with a car battery. The good news is, you don’t have to be an expert to spot problems. 

– Start with your nose

Does the battery smell like rotten eggs? If so, it’s probably leaking or cracked. If this is the case, your lead acid battery is potentially dangerous. Battery acid is actually sulfuric acid, and is extremely dangerous either touched or inhaled – as is the hydrogen gas it can produce. If your battery is in any way damaged, you should use our quick and easy quote-finder to get in touch with a trusted local garage for professional help.

– Is the battery hot to the touch?

If the battery case or the battery terminals is very hot, it could be an indication that it’s been working harder than it should have been. Lift the bonnet and let everything cool down before you charge the battery.

– Is there any corrosion on the battery terminals?

The battery’s ‘terminals’ are the two metal stumps that the leads attach to. Because of the material used to make the terminals and how they react with the air around them, they can sometimes become crusty with a green substance that builds up over time. It’s not really dangerous – but you should clean it to get the best connection between the battery charger and the battery before you start. A sandpaper pad will help you shift stubborn build ups.

Step 3 – Remove the battery from the vehicle

Car battery charging requires the battery to be removed from the vehicle. The good news is, this is usually fairly simple. 

You’ll need to start by removing the positive cable from the positive battery terminal. Both the positive terminal and negative terminal will be clearly marked on the battery – and it’s essential you remove them in the correct order. When the positive cable is off, you can remove the negative one. You’ll usually only need a small wrench to loosen the bolt on the clamp and wiggle it free from the terminal.

With the cables removed, you’ll then need to release the battery from the tray it sits on. This is different from vehicle-to-vehicle, but usually involves releasing it from a clamp that holds it in place.

When the battery’s released, you can lift it out. It’ll be heavier than you expect, so lift it properly and carefully – slipping a disc or dropping a 15kg battery on your foot isn’t going to make this any easier. 

Step 4 – Hooking up the car battery charger

Again, the specific instructions for each battery charger will vary from model to model – so be sure to read them thoroughly. Even years of experience isn’t a substitute for just reading the charger user manual!

Start by finding a safe, clutter-free, and well-ventilated area to work in.

You’ll need to start by plugging the charger in but making sure it’s turned off. Then, hook up the positive cable from the charger to the positive terminal on the battery. Next, hook up the negative cable from the charger to the negative terminal on the battery.

Some chargers have fast and slow options. Your charger’s instructions will go into how this technology works in more detail – but if you want the best possible result, it’s good to charge lead acid batteries on the slowest charge rate.

When everything’s safely connected and the charger’s switched to the slowest mode, you can turn the charger on a set the timer.

How long should you charge a car battery for?

There are lots of variables when it comes to charging a car battery. Honestly, it can take anywhere between a couple of hours and a full day to charge your battery, depending on the size of the battery, how much charge was left in it, and the power/type of charger you’re using.

If you’re looking for an example, consider this. Charging a regular car battery with a charge amp of around 4-8 amperes will take between 10-24 hours to get a full charge.

Most battery chargers have a gauge that shows how charged the battery is though – so you don’t usually have to guess – just keep an eye on the charger. 

Step 5 – When the battery is charged

When you’re confident that your battery is fully charged, it’s time to disconnect the charger and get it back into the car.

Essentially, you’re just going to be reversing everything you’ve just done. So, switch off the charger, disconnect the negative charger cable from the battery, then disconnect the positive cable. Then, lug the battery back to your car and carefully lift it back into position. 

You should secure the battery using the clamp, then connect and secure the negative cable to the negative terminal. When that’s in place, secure the positive cable to the positive terminal.

Now, the moment of truth!

As long as everything’s back as it should be, you’ll be able to jump in the driver’s seat and fire it up. Now, don’t be tempted to just fire it up a couple of times to test the charge – as the ignition process draws a lot of current from the battery. Leave the car idling for a few minutes when you’ve started it – giving the alternator chance to get some power back into the battery.

What about a jump start? Does that charge the battery?

Why bother with all this hassle when you can buy a pair of jumper cables from an auto parts store for less than $20?!

Well, connecting two cars to each other and jump-starting the vehicle isn’t really a charging method; it’s more of a ‘starting method’. Charging lead acid batteries takes a fairly long time, and you’re going to have to run your car for a long time for the alternator to get a meaningful amount of charge back into the dead battery after it’s been jumped.

Jump starting a car safely is another guide altogether – but it is something you have to be careful with. Misusing jumper cables can be dangerous for you – and can cause lasting damage to the battery, starter, engine management system, and other sensitive parts of your vehicle. If in doubt, recharge the battery using a dedicated battery charger.

We can help with car batteries!

If reading this battery charging guide has filled you with fear instead of confidence – don’t worry. Charging a car battery isn’t an essential life skill, and we’ve got partner garages near you who will be happy to help.

In fact, we can connect you with a trustworthy, hard-working local garage in less time than it takes to lift the bonnet. Click to get a quote from a mechanic, leave us some contact details – and that’s it! There’s no commission to pay us and no credit card details needed – you’ll deal directly with an outstanding local garage that’ll get you on the road again.