Driver Knowledge Tests

Should you let your car battery run right down?

In a vehicle with an internal combustion engine, a battery should have a life of around 5-6 years with regular use, but it depends on how you treat it.

The majority of batteries are now ‘maintenance-free’, but that doesn’t mean that there’s nothing you can do to improve battery life.

Vehicle batteries do best when they are kept charged. They are not designed to be used like a cellphone battery. Deep cycling, or letting the battery run almost flat then charging it again, is very damaging and will shorten the life dramatically.

When you leave your vehicle sitting, the battery is being gradually used by anything in your vehicle that requires electricity. This includes the clock, alarm, cellphone charger and an auxiliary equipment (larger trucks often have examples of these, such as safety lighting, electronic logbooks and items for driver comfort). This is called parasitic drain.

Keeping the battery clean is an important part of maintenance. Any corrosion that builds up around the terminals should be removed and the top of the battery wiped down. Dirt and grime sitting between the terminals can actually facilitate discharge, reducing the service life of the battery.

What happens when your battery starts to fail?

The signs of a battery that’s about to expire are:

  • Slow cranking – to start the vehicle, the battery operates the starter motor. When the battery is low, it might not have enough power to turn over the engine and, while the engine might fire, eventually it will not have enough power and you’ll just hear a clicking sound.
  • Illuminated battery light – this indicates that the battery is not charging and is usually a problem with the alternator, but it can come on if the battery is not providing power to the system. If the alternator has failed, this means the battery will gradually run out, even if you are already driving – using the lights will accelerate this. As we mentioned above, running the battery flat is not good for the battery.
  • No power when turning on the ignition – if the vehicle’s electronics don’t come on when you turn on the ignition, the battery has already failed.

After your battery dies, dispose of it properly. Most mechanics will have a method of disposing of it.

Are there special chargers for vehicle batteries?

You can get multi-stage battery chargers which will condition your battery and improve its overall health. These are used every couple of months.

Trickle chargers or battery maintainers can be used when vehicle sit for a long period of time, such as classic cars or show cars. Starting the vehicle occasionally and letting it idle for a few minutes will not be enough to maintain the battery’s charge.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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