The battery charges as you drive. The device which supplies the current is the alternator, driven from the engine by means of a V-belt. A faulty alternator causes the battery to discharge and disables the car. You can check the alternator by performing a battery charging test. The battery voltage should range between 13.8 V and 14.5 V. If it is too low, the risk of discharging increases. When it is too high, the battery may overheat causing the electrolyte to boil. A too high voltage may result from a faulty electrical system.
When to perform a battery charging test?
A battery test should be preformed by a garage during each periodical check-up and always whenever something is wrong with your battery. If the red battery indicator light goes on on your dashboard or when your battery is all the time undercharged (which you can tell by the car lights going out when you turn on the other car systems), you should check if the alternator provides the battery with the right charging current.
Where does the electrical power in your car come from?
Driven by a belt attached to the engine, the alternator is a complicated device responsible for providing current to the battery. In the period between the autumn and winter, when the air temperature drops, car batteries tend to lose their capacity. This plus using the numerous car devices, such as the fan, rear window heating or wipers may cause your battery to discharge very quickly. If the alternator is not working properly, your car will end up having no current and being disabled.
What is a battery test?
The purpose of a battery test is to check if the alternator provides power to the battery. It is performed by connecting a voltmeter to the battery and reading the voltage with the engine on. In the case of most cars this value should range between 13.8 V to 14.5 V. If it is lower, it means that the alternator is not charging the battery properly and may cause it to discharge. A higher value is also a reason to be concerned, as too high voltage may cause the battery to overheat and, consequently, result in the boiling of the electrolyte and even an explosion. Inadequate charging voltage may be due to a faulty voltage regulator in the alternator, also called the diode bridge, or a failure of the other alternator components.