A flat battery is the number one reason for roadside assistance call outs. It can be caused by something as simple as leaving a car door ajar through to something as complicated as ‘parasitic draw’. But the result is the same; that sinking feeling in the pit of your stomach as you turn the key in the ignition and nothing happens.
Causes of a flat battery
There are a number of reasons why batteries go flat:
- Lack of use – if you don’t use your car a lot, your battery will discharge itself over time (around 3% per month).
- Lack of maintenance – if you don’t keep your battery clean and maintained, it will let you down.
- Old age – batteries only last a few years, after which they start to go flat faster and eventually die.
- Overloading – leaving headlights, interior lights or the radio on while the engine isn’t running will quickly drain the battery.
- Alternator failure – the alternator charges the battery while the engine is running, so if the alternator fails, so will the battery.
- Extreme weather – batteries do not like extremes of hot or cold and can malfunction or die in extreme weather situations.
- Frequent short trips – if the car is used for frequent short trips, there may not be enough time for the alternator to properly charge the battery.
- Bad cables – if the battery cables are loose or broken, the battery may not make a good connection.
Another less well-known cause of battery failure is what is known as ‘parasitic draw’. This is where a load is being put on the battery even when the car is not being used. The only way to solve parasitic draw is to use a voltmeter to systematically check your electrical components including your alternator, accessory lights, fuses, radio and alarm, until you discover which is draining your battery without your knowledge. You might want to take your car to an auto electrician in such circumstances, as finding and fixing parasitic draw is a time-consuming task.
Flat battery remedies
If you find yourself stranded somewhere with a flat battery, there are a couple of things you can try before you call the auto club or mobile mechanic.
Firstly, check your battery terminals to make sure they haven’t come loose. The cable clamps must make a firm connection with the terminals at all times. Also make sure the battery hasn’t come loose in its harness, as this can lead to a bad connection.
Next check that the battery has water covering its plates. There should be an inspection port, or you can pop the plastic caps off and inspect the level through the holes. If there is insufficient water, top it up, but only use distilled water, as tap water could damage the battery’s cells.
- Have the other driver park their vehicle facing yours and raise both bonnets.
- Connect the positive jumper lead to the other car’s positive battery terminal (red) and connect the other end to your positive terminal.
- Connect the negative jumper lead to the other car’s negative terminal (black) and connect the other end to an unpainted metal area in your engine bay (e.g. the manifold).
- Have the other driver start and idle their vehicle and then start your vehicle as well.
NOTE: Do not attach the jumper leads the wrong way around or allow them to touch each other, as this may cause a short circuit which can fry sensitive onboard computers.
If none of these suggestions helps and there is no kindly stranger around, it’s time to call your friendly mobile mechanic or auto club technician. Nine times out of ten, they will give you a jump start as described here, or if the battery has died, will replace it with a new one.
Battery maintenance tips
Your car battery is designed to last around three years, although some can last as long as five and it should be replaced as part of your regular vehicle maintenance schedule. To ensure it lasts the full period and doesn’t let you down unexpectedly, you can observe the following maintenance tips:
- Clean your battery terminals – battery terminals get a white corrosive residue build-up over time. Remove the terminal clamps, clean off the residue with a toothbrush and a mixture of water and baking soda. You can also put petroleum jelly or other suitable lubricant on the clamps before tightening well.
- Maintain battery water level – keep an eye on your battery’s water level and top up with distilled water as required. Even if you have a modern battery that is sealed and maintenance-free, it will still have a water level indicator that you should monitor regularly.
- Give your car a run – if you use your car for lots of short trips, take it for a run in the country every now and then, as this will give the alternator the opportunity to fully charge your battery.
- Remove your battery – if your car is in storage or only used infrequently, remove the battery and store it in a dry place with evenly regulated temperature to prolong its life.