If you've been lucky enough to never have had to charge a car battery, the odds are you will someday. There are two common reasons why you'd need to use a car battery. The first is obvious: You left something on in the car that drained the battery. The second is the battery is near the end of its life. Nothing lasts forever, and even though a battery can last up to 10 years or more long, the fact is, after three to five years, depending on the quality, the battery starts to deteriorate.
How the Battery Works
The battery in a car provides enough amps to start the engine and then provide volts to electrical demands. Once the car engine starts and is running, the alternator restores the amps and voltage spent from the battery and provides constant backup for the battery. An alternator does not fully recharge a car battery, however, so when one is close to the end of its life, it does not put out enough amperage needed to turn the starter. Charging it will temporarily assist in getting the engine to start, but may not provide reliability on the next intended start-up.
Batteries contain a diluted solution of sulphuric acid, which has a chemical reaction to the lead plates that soak in it. This reaction makes the batteries volatile and susceptible to ignite if a spark occurs. A flammable mixture of hydrogen and oxygen escapes from the vents of the battery, so if you charge it incorrectly, you are risking a battery explosion.
Battery Charger Types
Several models of battery chargers are available. You get what you pay for. To properly and safely charge a car battery, you will need a 12-volt charger. Many low-line car battery chargers default at 12 volts, so there is no need to make an adjustment to settings for volts prior to charging. However, some high-line battery chargers may charge more than just car batteries, and, when this is the case, a 12-volt setting should be applied. Other settings on the charger may be deep cycle, maintenance free and conventional. Most car batteries, although maintenance free, would be considered conventional. The amp setting on the charger is important, and the owner's manual should be read in its entirety. High amp settings will charge the battery for quick starts, but are not as good for the life of the battery. Low amp settings will take much longer, but automotive batteries tend to hold a charge longer, without internal damage, when charged slowly over a longer period of time.
Charging the Battery
Do not plug the charger into an electrical socket first. Always connect it to the battery first to prevent live current through the battery clamps of the charger. Attach the red positive clamp to the battery first. Attach the black negative clamp to a ground away from the battery. This can be a non-painted metallic bolt head or bracket. Grounding away from the battery will minimise the risk of sparks occurring near the vents of the battery. Make the adjustments necessary to the battery charger dials and buttons and then plug it in. If applicable, set the timer or turn on the power switch. If you have to use an extension cord, be sure it's of equivalent grade to accommodate the charger. Set the timer on the charger or set a similar manual timer to check the battery when it goes off. To remove the charger, power it down first from the electrical source. Remove the black clamp first and then the red clamp. If you're going to start the car before powering down the charger, be sure the wires of the clamps are not able to come into contact with movable engine components.
To charge an uninstalled car battery, perform in the same way as above, but it would be wise to use a double-clamped jump lead to complete the connection between the charger and the negative terminal of the battery.