Between the electrolyte and the lead plates, a chemical reaction is created. This produces dangerous, explosive gases that vent through the battery cover vents. Because of this, caution should be taken when you charge or jump start a low battery. The same caution should also be taken every time you are working under the hood of your vehicle. It is important to provide as good ventilation as possible in the battery, so always keep it clean.
Your Cars Alternator. The cars alternator generates electricity which is employed to preserve battery storage charge and to lend a hand in operating the entire the electrical accessories, which includes the ignition and the engine control systems. The cars alternator is belt-driven by the engine and creates an alternating current which is transformed to twelve volts direct current by means of the rectifiers or diode bridge. In contradiction to popular idea, an alternator does not continuously generate electricity. It sequences on and off at the same time as demand goes up and down.
With other electrically powered features, the cause (and the fix) may not be so simple. Because of that, if any electric accessory stops working it's a good idea to first check whether a fuse that protects the circuit it's on has blown. The owners manual should show where a fuse for a particular feature is located (usually in a side panel below the dashboard near the driver's seat or under the hood). If you're handy with a multimeter that measures voltage, resistance and other things, you may be able to diagnose some of your own electrical problems. However, because they can be difficult for professionals to find and fix, they might be even harder for amateur technicians to solve.
Testing a battery's performance and reserve (or amp-hour) capacity is not just a matter of seeing whether it will hold a charge (or checking the electric eye found on some batteries to see if it is green), so testing is best done by an auto technician at a repair shop. A professional can also determine if any problems you are having may be caused by something else, like your battery terminals or alternator. If a bad battery is the culprit, your mechanic will help you choose and install an appropriate replacement.