Causes Of A Dead Car Battery

Usually the cause of a dead car battery (with no obvious reason such as lights being left on) is either a faulty battery or the battery is not being charged by the alternator. This could be because the alternator (the component which charges the battery) is faulty, or it could be because the belt which drives the alternator is slipping.

photo credit: Charles Williams

A quick way to check if the alternator is actually charging the battery is to start the car when it’s dark and switch on the headlights. Let the engine tick over at idle speed and look at where the headlights are shining. If the alternator is charging the battery OK, the lights should get brighter when you press on the accelerator and increase the revs. If the brightness doesn’t change, then it’s likely that the alternator isn’t charging the battery.

If the car battery is faulty, then it could be that it has just reached the end of its life. Batteries will usually last for between 3 and 5 years, depending on how fully they are charged. If you only do short trips in the car, the battery is going to spend most of its life at below full charge, and this will mean that the battery does not last as long as it would if you were doing longer trips and it was charging fully. If you have a multimeter (voltmeter) you can check the battery voltage with it. Touch the red multimeter lead to the positive battery terminal and the black lead to the negative battery terminal. With the engine off, the voltage should be between 12.5 and 12.8 volts. Start the engine, and when it is at idle speed the voltage should increase to between 13.6 and 14.3 volts. If the voltage does not increase, the alternator may be faulty.

If you are having starting problems, it could be due to loose battery terminal connections. Check that the red and black leads are tightly connected to the battery terminals. Another possible cause of starting problems is corrosion between the battery connections and terminals. If this is the case, they will need to be disconnected and cleaned. Make sure that the engine is off before you disconnect the battery.

The opposite type of car battery charger is the ‘fast charger’. This type of charger has an output of around 100-200 amps or  even greater, and can charge a flat (discharged) battery in under an hour. Fast chargers can cause the production of large amounts of internal heat inside the battery.  Fast chargers should really only be used by the professionals.

photo credit: Qfamily

Most car battery chargers on the market have an output range of 2 amps, 6 amps, 10 amps, and even as high as 50 amps at 12 volts. The output is usually adjustable and can give either a slower and longer charge or a fast charge to enable the car to be started within just a few hours.

Other types of charger can also be used, such as the car-to-car battery charger. This works in a similar way to jump-starting cables, but takes up less space when stored and is also easier to use. The device connects between the 12v sockets of the two cars, and the car with the good battery charges the flat battery, enabling starting of the car with the flat battery.

Trickle chargers are inexpensive and are unlikely to cause any damage to the car battery. They basically consist of a small transformer which plugs into the mains electricity outlet, and a pair of leads to connect to the battery. Trickle charging can take up to a few days to fully charge a dead battery, so it isn’t much use if you are in a hurry to start the car. Another type of trickle charger is the solar car battery charger, which has a small solar panel which produces enough charge to trickle charge the car battery through the 12v socket inside the car.

Rechargeable car battery chargers can be charged by mains electricity and then carried in the car, to be used to charge the battery even in areas with no power supply. Some of these chargers will have other features such as integrated torch, air compressor for inflating boats, air mattresses etc., pressure gauge, and charge indicator.

Whichever type of charger you choose, there are so many available that it’s a good idea to shop around to find the best price for the particular charger that you need.