A battery stores electricity for future use. It develops voltage from the chemical reaction produced when two unlike materials, such as the positive and negative plates, are immersed in the electrolyte, a solution of sulphuric acid and water. In a typical lead-acid battery, the voltage is approximately 2 volts per cell, for a total of 12 volts. Electricity flows from the battery as soon as there is a circuit between the positive and negative terminals. This happens when any load that needs electricity, such as the radio, is connected to the battery.

Most people don't realize that a lead-acid battery operates in a constant process of charge and discharge. When a battery is connected to a load that needs electricity, such as the starter in your car, current flows from the battery. The battery begins to be discharged.

In the reverse process, a battery becomes charged when current flows back into it, restoring the chemical difference between the plates. This happens when you're driving without any accessories and the alternator puts current back into the battery.

As a battery discharges, the lead plates become more chemically alike, the acid becomes weaker, and the voltage drops. Eventually the battery is so discharged that it can no longer deliver electricity at a useful voltage.

You can recharge a discharged battery by feeding electrical current back into it. A full charge restores the chemical difference between the plates and leaves the battery ready to deliver its full power.

This unique process of discharge and charge in the lead-acid battery means that energy can be discharged and restored over and over again. This is what's known as the cycling ability in a battery.

When you ask yourself "Why won't my car start?" you usually refer to the battery as being "dead, even though that's not technically correct. A battery that's merely discharged-from leaving your headlights on or from a damaged alternator-can be recharged to its full capacity. But a battery that's at the end of its service life can't be recharged enough to restore it to a useful power level. Then it truly is dead, and must be replaced.

If the battery is discharged and not dead, you can jump-start it from another fully charged battery. But if the alternator or another part of the electrical system in your car is damaged, the battery will not recharge and neither a mechanic nor a service station will be able to recharge it. So if your battery keeps discharging, have your electrical system checked before you replace it. What looks like a bad battery could be an electrical system problem. If you have a bad component in the electrical system, it will keep draining a new battery, and you'll be stranded again and again.

How do you know which battery is right for your car? Here are some quick tips to help you make the right choice.

Check your vehicle manual for the original equipment manufacturer's recommendations for.

• Battery group size - the battery size that will best fit the physical dimensions of your vehicle. Many vehicles can accommodate more than one group size.

• Amps hours (AH) - it's the unit of measure for a battery's electrical capacity when continuously discharged over a period of 20 hours before the voltage fails to 10.5V.

• Cold cranking amps (CCA) - CCA is critical for good cranking ability. It's the number of amps a battery can support for 30 seconds at a temperature of -18 degrees Celcius until the battery voltage drops to unusable levels.

• Reserve capacity (RC) - helps to power your vehicle's electrical system if the alternator fails. It identifies how many minutes the battery can supply ample power without falling below the minimum voltage needed to run your vehicle.

In general, for both CCA and RC, the higher the number the better. However, if you live in a cold climate, the CCA rating should be an important consideration in choosing a battery. Conversely, if you live in a high heat climate, you don't need as much CCA.

If you're looking for a deep-cycle battery for marine, you must also consider.

• The type of equipment to be powered

• The number of amps needed to run the equipment

• The number of hours you'll be using the equipment

When fitting and handling batteries, please make sure you and your colleagues are aware of the safety and handling by following all the safety recommendations and advice below.

Danger of exploding batteries

Batteries contain sulphuric acid and produce explosive mixtures of hydrogen and oxygen. Because self-discharge action generates hydrogen gas even when the battery is not in operation, make sure batteries are stored and worked on in a well-ventilated area.

• Always wear ANSI Z87.1 (U.S.) or CE EN166 (Europe) approved safety glasses and face shield or splash-proof goggles when working on or near batteries.

• Always wear proper eye, face and hand protection.

• Keep all sparks, flames and cigarettes away from the battery.

• Never try to open a battery with non-removable vents. (See Fig. 1 for the acceptable wording and symbols currently used on vent caps.)

• Keep removable vents tight and level except when servicing electrolyte.

• Make sure work area is well-ventilated.

• Never lean over battery while boosting, testing or charging.

• Exercise caution when working with metallic tools or conductors to prevent short circuits and sparks.

Safe Charging

NEVER ATTEMPT TO CHARGE A BATTERY WITHOUT FIRST REVIEWING THE INSTRUCTIONS FOR THE CHARGER BEING USED. In addition to the charger manufacturer's instructions, these general precautions should be followed for safe charging.

• Always wear proper eye, face and hand protection.

• Always charge batteries in a well-ventilated area.

• Keep vents tight and level.

• Turn the charger and timer "OFF" before connecting the leads to the battery to avoid dangerous sparks.

• Never try to charge a visibly damaged or frozen battery.

• Connect the charger leads to the battery, red positive (+) lead to the positive (+) terminal and black negative (-) lead to the negative (-) terminal. If the battery is still in the vehicle, connect the negative lead to the engine block to serve as a ground. Be sure the ignition and all electrical accessories are turned off. (If the vehicle has a positive ground, connect the positive lead to the engine block.)

• Make sure that the charger leads to the battery are not broken, frayed or loose.

• Set the timer, turn the charger on and slowly increase the charging rate until the desired ampere value is reached.

• If the battery becomes hot, or if violent gassing or spewing of electrolyte occurs, reduce the charging rate or turn off the charger temporarily

• Always turn the charger "OFF" before removing charger leads from the battery to avoid dangerous sparks.

Handling battery acid

Battery acid, or electrolyte, is a solution of sulphuric acid and water that can destroy clothing and burn the skin. USE EXTREME CAUTION WHEN HANDLING BATTERY ACID and keep an acid-neutralizing solution - such as baking soda or household ammonia mixed with water-readily available. When handling batteries.

• Always wear proper eye, face and hand protection.

• If the electrolyte is splashed into an eye, immediately force the eye open and flood it with clean, cool water for at least 15 minutes. Get prompt medical attention.

• If electrolyte is taken internally, drink large quantities of water or milk. DO NOT induce vomiting. Get prompt medical attention.

• Neutralize with baking soda any electrolyte that spills on a vehicle or in the work area. After neutralizing, rinse contaminated area clean with water. To prepare electrolyte of a specific gravity, always pour the concentrated acid slowly into the water, DO NOT pour water into the acid. Always stir the water while adding small amounts of acid. If noticeable heat develops, allow the solution to cool before continuing to add acid.