Motoring

What you need to know about car batteries

RACV mechanic attending a callout to a dead car battery

RACV

Posted June 10, 2024

Find out everything you need to know about car batteries, from how to avoid draining the battery and shortening its life to signs that it's time for a replacement.

Battery failure is a common cause of car breakdowns, with RACV Emergency Roadside Assistance attending more than 250,000 callouts in Victoria for this reason alone in 2023.

"RACV battery callouts resulted in 130,162 car battery replacements and over 120,000 jump-starts or tows, so it is worth reading up on car battery care," says RACV General Manager Motoring Products Jeff Ames.

“Car batteries are more likely to go flat in winter and during prolonged cold weather. The chill slows down the chemical reactions inside your car battery, sapping its strength, meaning it must work much harder to produce electricity," Ames says.

Vehicle maintenance is especially important in winter as inclement weather like cold temperatures, wind, ice, sleet, and snow become more common.

To help prevent your battery from going flat in the first place, read up on car battery warning signs, charge levels and more with this handy guide.

Everything you need to know about your car battery

What does a car battery do?

Car batteries are responsible for starting your car and powering your vehicle's lights. When you turn your car key in the ignition or push the start-stop engine button, you are sending a signal to your car to activate its starter motor. The battery then creates a chemical reaction, which generates a large, short burst of electrical energy to the car’s starter motor, allowing it to crank the engine to life. This electricity also powers your car’s lights and other accessories like phone chargers, infotainment screens, parking cameras and heated seats.

Once the engine is running, your car’s alternator sends the electric current back into the battery to maintain its charge. If a battery is fully discharged (depleted) without being recharged by the alternator as you drive, it fails.

 

Check Battery warning light on car dashboard

Keep an eye out for the 'Check Battery' warning light on your car's dashboard. Image: Getty

 

How do I know if my car battery is low?

These are the warning signs that your car battery may soon need charging or replacement:

  • ‘Check battery’ dashboard light – older cars may display the ‘check engine’ light instead, but all newer cars should have a specific 'check battery' light

  • Slow or 'coughing’ engine crank – a worn-out battery could struggle to deliver the starter enough electricity to crank the engine

  • Dim lights, slow windscreen wipers, silent radio or dead remote locks – low batteries may not be able to provide the same level of power to your electronics

How do I check my car battery's charge level?

You can purchase a multimeter device from most automotive shops. The multimeter will test your car battery’s voltage and give you a reading. To get the most accurate reading, test your battery after your car has been turned off overnight. Set your multimeter to read DC volts and turn the dial to 20, then touch its red probe to the positive (+) terminal and its black probe to the negative (-) terminal on your car battery.

Here’s how to make sense of your car battery’s voltage readings:

  • 12.6v = 100% (fully charged)

  • 12.4v = 75% (charged)

  • 12.2v = 50% (discharged/flat)

  • 12v = 25% (flat/dying)

  • 11.9v = 0% (dead)

Anything under 12.4v is considered discharged: the battery may fail at any point.

 

RACV mechanic testing car battery as driver watches from the footpath

A roadside assistance specialist can help you jump-start your flat car battery or install a new one if the battery is too old.

 

How do I know if my car battery is dead?

Most drivers only realise their car battery has died when they go to turn on their car and it won’t start. Your engine may try to crank, in which case you will hear a clicking sound, but it will not come to life.

Why has my car battery gone flat?

There are several reasons why your car battery might have gone flat. The most common include:

  • End of lifespan – most car batteries are designed to last between two and six years.

  • Leaving your lights on – forgetting to switch off your headlights or cabin lights can quickly drain your battery.

  • Only driving short trips – since your battery is charged by the alternator as you drive, short driving distances (under 20 minutes) won’t allow for much recharging time.

  • Leaving your car parked for a long time – your car uses a small amount of current when the key is not in the ignition; so, without the alternator recharging the battery as you drive, the battery will drain over time.

  • Extreme temperatures – unusually hot or cold weather can weaken battery performance.

  • Faulty parts – issues like battery cable corrosion, loose cables, battery leaks, faulty charging and defective fuses can all shorten your battery’s lifespan.

How do I jump start my car?

Safely jump starting your vehicle can recharge your dead car battery. Be aware that if your battery has deteriorated from corrosion or extreme weather conditions, or simply reached the end of its lifespan, it will quickly run out of charge again. If your battery dies again a short while after being jump-started, it may be time for a new battery.

Here’s how to jump start your car:

  • Get a friend to park their car with a charged battery close to yours.

  • Put both cars in park (for autos) or neutral (for manuals) with the handbrakes on and engines off.

  • Open both car hoods and get out your jumper cables – there should be a red cable and a black cable.

  • Attach the red cable with one clamp on each car battery’s positive terminal.

  • Attach one clamp on the black cable to the charged battery’s negative terminal.

  • Attach the other black clamp to a piece of bare, unpainted metal on the car with the dead battery, such as a nut on the engine block.

  • Start the charged car’s engine and wait for one minute.

  • Start the discharged car’s engine and leave both cars running for several minutes.

  • Disconnect the cables in the reverse order you attached them.

  • Drive your car for 10-20 minutes to ensure that the charge is retained.

If you need help to jump start your vehicle, or if your car won’t turn on after a jump start, call a mobile roadside service like RACV Emergency Roadside Assistance. Please refer to your car's manual for model-specific instructions.

 

RACV ERA worker attaching jumper cables to a car with a dead battery

RACV Emergency Roadside Assistance vehicles are equipped with quality jumper leads to safely revive a flat battery.

 

How do I get a replacement car battery?

If your car battery is flat, a mobile car battery service can get you back on the road in no time. RACV's mobile car battery service is available across greater Melbourne and Geelong. You don’t need to be an RACV Member to get a quote or book the service. Or you can sign up for RACV Emergency Roadside Assistance, which provides breakdown support for mechanical issues and problems like punctured tyres, lockouts and flat batteries.

Which car battery do I need?

Your best bet is to check your vehicle manufacturer’s owner manual or talk to your roadside assistance provider. Installing an incorrect battery in your car can severely damage its electrical system.

If you can’t find your owner's manual, you will need to know your battery’s group size to ensure that the new battery fits in the vehicle battery case. You can find the group size on your old battery’s label: it will be a two-digit number, sometimes followed by a letter.

Check the manufacture date on any battery you're thinking of purchasing. You should not buy a car battery older than six months from the manufacture date, considering the average battery lifespan is two to six years.

There are several types of car batteries, including lead-acid battery variants, lithium-ion batteries, and nickel-metal hydride (NiMH) batteries. Which variant you should use depends on your vehicle’s make and model.

mechanic sorting through car batteries in the back of his van

If your car battery is dead, you should call a trusted roadside assistance service.

 

How do I take care of my car battery in cold weather?

A fully charged lead-acid battery is more resistant to the cold than a partially discharged battery. "A charged battery will not freeze until temperatures drop to -50°C, whereas a battery with a low charge can freeze at -1°C," Ames advises.

If your battery freezes, the water inside expands and causes irreparable damage to the cells. Luckily, there are a range of things you can do to help prevent your battery from freezing in the first place.

"Look out for a Cold-Cranking Amperage (CCA) rating when buying an automotive battery, which tells you how well the battery performs in cold weather when fully charged," Ames says. 

A battery’s CCA rates how much current a battery can deliver for 30 seconds at -18°C without dropping to a specified cut-off voltage.

"To protect your car battery in cold weather, park your car in a garage rather than on the street if you can, especially overnight or in high winds," Ames says.

"You can also purchase a battery blanket online to keep your battery warm, but checking that the battery is fully charged is a fantastic way to prevent breakdowns."

 

At home or on the road, our mobile car battery replacement service can come to you.
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