Complete Guide on Charging a Car Battery - All You Need To Successfully Charge a Car Battery

If you’ve experienced a dead car battery due to leaving car accessories on whilst idling such as a light or AC then it may be time to recharge your battery.

In order to effectively charge a car battery, it's ideal to use a car battery charger that is designed to intelligently charge your car battery in order to maximise its lifespan. Sometimes driving it around for a short period of time is not recommended, this is called 'surface-level charging' and can end up doing more harm than good.

Charing a car battery can be straightforward with the correct charger, we recommend using a smart charger as the charger automatically regulates the amount of amperage (AMPS) that is required to get it back to full capacity. Investing in a smart charger can allow the battery to exceed standard lifespan expectations and increase the likelihood of greater long-term performance.

How do I know If my Battery Requires Charging?

If you have a battery tester you can directly find out the Voltage, Amps & Cold Cranking Amps (CCA). If you do not own a battery tester you can perform a basic diagnosis using a multimeter, the voltage level can have an effect on the longevity of your battery if your battery is constantly fully charged then it will perform much longer than the ones that are undercharged.

Here is a rundown on what voltage readings mean when you test your battery:

• 12.6V or more - Fully charged & healthy
• 12.5V - Stable but charging recommended (check the voltage again in a few days)
• 12.1V - 12.4V - Partially discharged and requires charging
• 12.0V or less - Flat & needs immediate charing or will die soon

If you require professional testing, at My Battery Plus we offer this service free of charge - you can book in and our team members can have your battery professionally tested.

Another method is to use the hydrometer built-in within the battery to identify the current state of the battery, you can check as indicated by the manufacturer's label usually located at the top of the car battery.

You can use a hydrometer on non-maintenance-free batteries or located a built-in hydrometer on maintenance-free batteries. The hydrometer is used to identify the current state of charge, with maintenance-free batteries which are usually located at the top where the handle sits.

Here is what the indications mean:

If the indicator is green, it means that the battery is charged and requires no additional charge, however, to confirm you should use a tester and evaluate the numbers – if a low voltage appears continue to charge.

Dark green or black usually means that it requires charging, the electrolyte solution has undergone a chemical reaction, and gasses have escaped through the relief valves, this leaves the solution closer to water and it requires charging to recondition it back to a state of reactivity with the plates.

Clear or white means that the electrolyte solution has lost its state of charge and may contain a dead cell. If you have a non-maintenance free battery, you can proceed to unscrew the caps located at the top of the battery and fill it up with distilled water, then proceed to place the battery back in charge once water levels have been topped off.

If you have a maintenance-free battery, it is recommended that you replace it once you see the clear indicator, if you require a quote for a replacement feel free to give our team a call.

How to choose what car battery charger to use?

It is important to purchase or use a car battery charger that is right for your battery, there are various battery chargers out there with different purposes. The difference is in their function as there is not just one way of charging a car battery.

Choosing the right car battery charger is important, there isn't just one charger out on the market and different chargers are built for various modes of charging. The main difference between chargers is the rate and method which provides the voltage and amperage flow to the battery.

Here are a few charger types out on the market.

Simple Battery Charger

This is a charger that provides direct current (DC) power to a battery, the charge is constant and does not include a timer function that alters the rate of current output, which can take longer to charge a battery.

Trickle Battery Charger

This charger uses a method that provides a low current charge over long periods of time and is safe to leave on your car battery for extended amounts of time.

Timer-based Battery Charger

This charger uses a timer-based setting and stops after the time limit is reached. Proceed with care as leaving it on for more than it is supposed to can cause irreversible damage to the car battery.

Intelligent Battery Charger

This charger uses a technology that is able to identify what level of charge the battery requires, and adjusts its level of current output through communicating with the battery - offering optimised electrical outflow when connected. When the battery has reached its full state of charge it automatically switches off.

How to get started charging your car battery

Prepare your gear

Safety first, always. Grab yourself a pair of protective goggles and gloves to ensure you don’t get anything into your eyes or on your hands, this is an important step because failing to protect yourself when working with automotive vehicles and the dangerous chemicals that come with it can cause fatal injury.

You can choose nitrile, neoprene, or natural rubber latex when handling chemicals for maximum protection. For your choice of eyewear, a standard clear plastic goggle ensures nothing gets into your eyes whilst working under the hood.

Remove your battery from your vehicle

You may charge the battery whilst it is secured in its tray, however, for the sake of convenience as some car batteries are hard to get to it is best to remove it altogether.

Remove the negative terminal first and then move onto the positive terminal next. Once that is done remove your battery by lifting it at an upright position and placing it somewhere safe to charge.

If you can’t locate your battery refer to the owner’s manual as some car batteries can be hidden away under other engine parts under the bonnet or even in the trunk.

Check the terminals and give them a clean

Inspect and clean the battery terminals, this is done by identifying whether or not there is build-up around the terminals, this is an important step you don’t want to miss as build-up can lead to a weak connection and can ultimately lead to quicker battery failure.

It is recommended to use a terminal cleaner for maximum results, if you are unable to attain a terminal cleaner you can mix baking soda with water and disperse the solution around the terminals, then proceed to clean it with sandpaper – ensure you’ve cleaned it under you see clear bare metal.

Cleaning is crucial for maintaining a strong connection and allowing electricity to flow optimally, so make sure you don’t skip this step.

If you find a dry, white crystal-like substance around the terminals this is a sign that it definitely needs a clean, this is called ‘sulfation’ and occurs when a battery has poor charge.

Set up your charger and connect it to your battery

Find a secure flat surface for both your battery and charger to sit on, this surface should be sturdy to ensure that it won’t disconnect any of the cables during the battery charging process, before plugging it into the charger also make sure that the place you plan on charging it has proper ventilation.

Once that is done begin to connect your cables to the battery itself, do this by connecting the cable with the battery terminals, the positive terminal first (+), and then proceed to connect the negative terminal second (-). If you’re not sure which one is positive or negative look at the terminals, they are usually marked right next to them.

Make sure this is done in the correct order with both cables connected to the correct terminal, if you do not do this correctly then you may potentially damage your battery or charger and in extreme cases cause a fire. One final check to see if the cables are attached firmly and you’re good to leave your car battery charging.

Common Questions About Battery Charging

Charging Can you leave a car battery charger on too long?

With a simple charger, the short answer is yes, even at a rate of 2amps the battery will eventually die. The science behind it is simply turning the electrolyte solution within the battery into a gas, it happens when the electrolyte gets hot (both hydrogen and oxygen) and gases are generated as a result.

With older batteries that have ventilation in their cases overcharging can cause the electrolyte to cook leaving the plates exposed and vulnerable to corrosion. Newer batteries that use SMF (sealed maintenance free), overcharging can cause a chemical build-up of gasses resulting in an explosion.

Is it safe to leave a trickle charger on overnight?

Most high-quality trickle chargers are left on a battery to restore the battery to its maximum capacity, this type of charger usually slow charges batteries and then automatically stops when the battery is at full charge.

This is a major advantage of trickle chargers and can be safely left overnight for it to charge as its in-built auto-shut-off mechanism can identify when the battery is full or not.

Can a completely dead battery be charged?

This depends, if you’ve taken care of your battery and have maintained it throughout its lifecycle then the answer is more than likely yes, you can revive a dead battery simply by charging it. In the event that it doesn’t charge or hold maximum capacity you are left with no option but to replace it.

If you’re experiencing this then it’s more than likely that your battery is at the end of its lifecycle and will require it to be replaced, for a proper diagnosis you can have it checked by our experts or replaced here.

Is it OK to charge a car battery while connected?

You can charge your car battery while it is still connected to your vehicle, doing this does require precaution. Ensure you are wearing your safety gear and check the voltage on your power supply, make sure that it doesn’t exceed 14.7 volts, if you can use a smart charger as they are the safest option for this method.

Also inspect the battery beforehand checking if there are any leaks or cracks in the battery, if you do see any then replace it immediately as this is a safety hazard.

If you have any more questions or concerns about charging, feel free to contact us and get expert advice.