subject: Common Causes Of A Flat Car Battery [print this page] You get into your car and turn the key, but instead of the engine firing into life, nothing happens. You then realise that you have a flat car battery. If it's something simple like you forgot to turn off the lights, a short time hooked up to a car battery charger will make everything ok again. If there is no obvious reason for the battery being flat, this is more of a problem.
If you cannot see any obvious reason for the battery being flat, for example the lights were left on, it may be that the car battery is not being charged by the alternator (the part of the car which generates electricity for the battery). It could be that the belt which drives the alternator is loose or the alternator may be faulty.
One way to quickly check to see if the alternator is charging the battery is to start the engine then switch the headlights on. With the engine ticking over, press the accelerator pedal and see if the headlights get a bit brighter. If they do, it means that the alternator is probably working and the fault is with the battery. If the headlights stay the same brightness, it is likely that the alternator is faulty.
Vehicle batteries usually last for a few years before needing to be replaced. The life of the battery will vary depending on how fully it gets charged while driving. Short trips do not charge the battery fully whereas long trips will charge the battery completely. Those batteries which get charged fully while driving tend to last longer than ones which don't get charged fully. The occasional use of a car battery charger to fully charge the battery will increase its useful life.
It is possible to test the car battery using a voltmeter. The voltmeter lead which is red needs to touch the positive terminal of the battery and the black lead needs to touch the negative battery terminal. When the engine is switched off the voltage should be from 12.5 to 12.8 volts. This should increase when the engine is running to between 13.6 and 14.3 volts. A voltmeter reading which does not change when the engine is running means that a faulty alternator is likely.
If you are having problems with starting, this could also be due to loose connections on the battery terminals. Check both connections at the battery terminals to make sure that they are tight. It is a good idea to also check for corrosion between the terminals on the battery and the connections. If there's any corrosion, clean the corrosion off, re-connect the terminals and apply some grease or petroleum jelly to the top of the connections to keep out moisture.
