The automotive battery, also known as a "lead-acid storage battery", is an electrochemical device that produces voltage and delivers current. In an automotive battery we can reverse the electrochemical action, thereby recharging the battery, which will then give us many years of service. The purpose of the battery is to supply current to the starter motor, provide current to the ignition system while cranking, supply additional current when the demand is higher than the alternator can supply, and act as an electrical reservoir.
The automotive battery requires special handling. The electrolyte (water) inside the battery is a mixture of sulfuric acid and water. Sulfuric acid is very corrosive; if it gets on your skin it should be flushed with water immediately. Likewise, if it gets in your eyes it should be flushed with a mild solution of baking soda and water immediately and you should see a doctor as soon as possible. Sulfuric acid will eat through clothing, so it is advisable to wear old clothing when handling batteries. It is also advisable to wear goggles and gloves while servicing the battery. When charging, the battery will emit hydrogen gas. It is therefore extremely important to keep flames and sparks away from the battery.
Because batteries emit hydrogen gas while charging, the battery case cannot be completely sealed. Years ago there was a vent cap for each cell and we had to replenish the cells when the electrolyte evaporated. Today's batteries (maintenance-free) have small vents on the side of the battery cover. The gases emitted have to go through baffles to escape. During this process the liquid condenses and drops back to the bottom of the battery. Normally there's no need to replenish or add water to the battery.
Today's batteries are rated in "cold cranking amps". This represents the current that the battery can produce for 30 seconds at 0 degrees before the battery voltage drops below 7.2 volts. An average battery today will have a CCA (Cold Cranking Amps) of 500. With the many different makes and models of cars available today, batteries will come in many different sizes, but all sizes come in many CCAs. Make sure you get a battery strong enough to operate properly in your car. The length of the warranty is not indicative of the strength of the battery.
Battery cables are large diameter, multi-stranded wires which carry the high current necessary to operate the starter motor. Some battery cables will have a smaller wire soldered to the terminal, which is used to either operate a smaller device or to provide an additional ground
Even maintenance-free batteries need periodic inspection and cleaning to insure they stay in good working order. Inspect the battery to see that it is clean and that it is held securely in its carrier. Some corrosion may collect around the battery. Electrolyte condensation contains corrosive sulfuric acid, which eats away the metal of battery terminals, cable ends and battery hold-down parts. To clean away the corrosion, use a mixture of baking soda and water and wash all the metal parts around the battery. Rinse with water. Remove the battery cables from the battery (negative cable first) and wire brush the inside of the cable end and the battery post. Reinstall the cables (negative end last) and coat all exposed metal parts (paint or grease can be used).