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Car Batteries

A car battery is principally used to start the engine. It is also used to filter or stabilize power and to provide extra power for the ignition, lighting and other accessories when their combined load exceeds the capability of the charging system, i.e., when the engine is idling. It also provides power to the electrical system when the charging system is not operating. The battery lies hidden under the bonnet and is an essential component of your vehicle. Regular care is a must, for if it in bad shape, the car will refuse to move. "Push-start" is a solution but cannot be carried on for long. A well-maintained battery lasts for two years. Regular care of your battery is a must, otherwise your car will not move. "Push-start" is an option but not a long term solution. A well maintained battery usually lasts for two years.

Points to note when buying a new battery
Climatic conditions determine the kind of battery you should buy. Colder climates require batteries with higher CCA ratings than in a hot climate.

Cold Cranking Amps (CCA)
The most important consideration is sizing the battery's CCA rating to meet or exceed, depending on the climate, is the car's OEM cranking requirements. CCA's are defined as the discharge loads measured in amps that a fully charged battery at 0 degrees F (-17.8 degrees C) can deliver for 30 seconds while maintaining the voltage above 7.2 volts.

Batteries are sometimes advertised by their Cranking Performance Amps (CA) or Marine Cranking Amps (MCA), which is measured at 32 degrees F (0 degrees C) or Hot Cranking Amps.

HCA is measured at 80 degrees F (26.7 degrees C), which is not the same as CCA. Do not be misled by CA, MCA or HCA ratings. Multiply the CAs by 8 to convert Cas to CCAs. To convert HCAs to CCAs, multiply HCAs by 0.69.

Buying batteries with double or triple CCA ratings that exceed the OEM requirement are a waste of money for hot climates. However, in colder climates the higher the CCA rating the better, due to increased power required to crank a sluggish engine and the inefficiency of the cold battery. As batteries age, they are less capable of producing CCAs.

One of the major battery manufacturers, Exide, publishes the following table:
Available Power from battery Temperature Degrees F Power Required to crank engine
100% 80 100%
65% 32 155%
40% 0 210%
25% -32 350%
If more CCA capacity is required, two (or more) 12 volt batteries can be connected in parallel. Within a BCI group size, generally the battery with more CCA will have more plates because a larger surface area is required to produce the higher current.

Reserve Capacity (RC)
The Reserve Capacity rating is the second most important consideration while buying a battery. This is because of the effects of an increased parasitic (key off) load and in emergencies. Reserve Capacity is the number of minutes a fully charged battery at 80 degrees F (26.7 degrees C) can be discharged at 25 amps until the voltage falls below 10.5 volts. More RC is better in every case! In a hot climate, for example, if your car has a 360 OEM cranking amp requirement, then a 400 CCA rated battery with 120 minute RC with more electrolyte would be more desirable than one with 1000 CCA with 90 minutes of RC. If more RC is required, two six-volt batteries can be connected in series or two (or more) 12 volt batteries can be connected in parallel. Within a BCI group size, generally the battery with larger RC will weigh more because it contains more lead.

Type of Batteries

Low maintenance (non-sealed) and maintenance free (non-sealed or sealed) are the two most common types of car batteries.
The advantages of maintenance free batteries are less preventative maintenance, longer life, faster recharging, greater overcharge resistance, reduced terminal corrosion and longer shelf life, but they are more prone to deep discharge (dead battery) failures due to increased shedding of active plate material.

In hot climates, buying non-sealed batteries is recommended because a sealed battery will not allow you to add water when required, or to test the specific gravity with an external hydrometer. Some manufacturers introduced a third type of car battery, "dual", that combined a standard battery with switchable emergency backup cells. For about the same cost a better approach was to buy two batteries and isolate them.

It is best to buy a commercial or AMG battery for excessive vibration applications. Car batteries are specially designed for high initial cranking amps (usually for five to 15 seconds) to start an engine; whereas, deep cycle (or marine) batteries are designed for prolonged discharges at lower amperage.

A "dual marine" battery is a compromise between a car and deep cycle battery; However, a car battery will give you the best performance in a car. For RVs, a car battery is used to start the engine and a deep cycle battery is used to power the accessories. The batteries are connected to a diode isolator and both are automatically recharged by the RV's charging system when engine is running.

Batteries are generally sold by model, so the group numbers will vary for the same price. This means that for the SAME price you can potentially buy a physically larger battery with more RC than the battery you are replacing, e.g. a 34/78 group might replace a smaller 26/70 group and give you an additional 30 minutes of RC.
If you do this, be sure that the replacement battery will fit, the cables will connect to the correct terminals, and that the terminals will NOT touch the hood when closed.

BCI and the battery manufacturers publish application guides that will contain the OEM cranking amperage requirements and group number replacement recommendations by make, model and year of car, and battery size, CCA and RC specifications. Manufacturers might not build or the store might not carry all the BCI group numbers. To reduce inventory costs, dual terminal "universal" batteries that will replace several group sizes are becoming more popular and fit 75% or more of cars on the road today.


Determining the "freshness" of a battery is sometimes difficult. A battery that is more than six months old should never be bought because it begins to sulfate. Sulfation occurs when lead sulfate can not be converted back to charged material and is created when discharged batteries stand for a long time or from excessive water loss.


As with every thing else, it is necessary that you check the warranty period of the battery before you buy it.

It is extremely important to note that

batteries contain a sulfuric acid electrolyte, which is a highly corrosive poison. It produces gasses when recharged and explode if ignited. When working with batteries, you need to have plenty of ventilation, remove jewelry, wear protective clothing and eyewear (safety glasses), and exercise caution. Whenever possible, you are requested to follow the manufacturer's instructions for testing, jumping, installing and charging.


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