What to know about your car battery

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 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.

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.

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 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 mechanic like RACV Emergency Roadside Assistance. Please refer to your car's manual for model-specific instructions.

How do I get a replacement car battery?

If your car battery is flat, a mobile car battery replacement service can get you back on the road in no time. In the Greater Melbourne or Geelong area, RACV Batteries can come to your home, office or roadside car 24 hours a day, seven days a week. You don’t need to be an RACV Member to access RACV Batteries. Get a quote for fast delivery, experienced mechanics, hassle-free replacement and an extensive range of car batteries with three-year warranties and price match guarantees.

Which car battery do I need?

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

If you can’t find your owner 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.

Make sure to check the manufacture date on any battery you are thinking of purchasing. You should not buy a car battery older than six months from 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 exact variant you should use depends on your vehicle’s make and model.

How much does a car battery cost?

Car batteries vary in price depending on your car model and make. RACV Batteries are competitively priced, including a Price Match Guarantee, and include delivery and installation.