subject: Common Flat Car Battery Causes [print this page] After getting into your car you turn the key to start the engine but nothing happens. At that moment you realize that your car's battery is flat. It could be something simple such as forgetting to turn off the lights, in which case once the battery has been charged again everything is OK. However, there may be no obvious reason why the car battery has become flat, and this is more problematic.
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.
An easy way to check if your alternator is working and charging your battery is to start the car engine and switch on your headlights. While the engine is running, push down the accelerator pedal while you are watching the headlights shining on a wall or something similar. If the alternator is working the lights will get brighter as the engine speeds up. If the brightness does not change it is probable that the alternator has a fault.
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.
The battery can be tested by using a voltmeter. The red voltmeter lead should touch the positive battery terminal and the black lead should touch the negative terminal. With the engine off, the voltmeter reading should be between 12.5 and 12.8 volts. With the engine running the voltage should increase to between 13.6 and 14.3 volts. If the reading does not change it means that the alternator is probably faulty.
If you have starting problems it could be as a result of loose battery terminal connections. Check the connections of both battery terminals to ensure that they are sufficiently tight. It may also be useful to inspect for corrosion between the connections and the battery terminals. Any corrosion should be cleaned off and when the connections are re-fitted some petroleum jelly or grease should be applied to the top of the connections to prevent water from entering.
