i found this, so im passing it on.....



Car Batteries

What you need to know about your vehicle's battery.

Most of us don't think much about the battery in our vehicle; we simply turn the key and expect the engine to start. We expect the battery to be reliable, long-lasting and maintenance-free. Once it fails, however, odds are you'll have to replace it, and knowing which type and size battery you need is important. Will it be conventional, maintenance-free or recombination?
Conventional Batteries
A 12-volt automotive battery has six compartments or cells. Each cell has a series of alternating positive and negative plates separated by isolators. All negative plates in the battery are connected, as are all positive plates.

Each plate has lead sheeting bonded to it and every cell is filled with a solution of sulfuric acid and distilled water (electrolyte). As the battery supplies electricity, or discharges, the electrolyte reacts with the lead, forming lead sulfate and weakening the electrolyte.

Conversely, as it charges, the acid is returned to the electrolyte and the lead sulfate is converted back into active material in the plates. During this cycle, hydrogen, and oxygen molecules evaporate out of the electrolyte, which is why batteries often need topping up with distilled water. Over time, continual charge/discharge cycles slough lead off the plates that build up in the bottom of the battery. Eventually, the plates short out and the battery dies.

Maintenance-free Batteries
A maintenance-free battery is essentially the same as a conventional battery, except for thicker plates and more electrolyte. Most new vehicles come equipped with this type of battery since it is more reliable and lasts longer. However, these batteries cannot be topped up and once the electrolyte evaporates and the plates are exposed, the battery is no good.

Another type of maintenance-free battery is the gel-type. It has the electrolyte in gelatin form and does not lose electrolyte through evaporation. However, because the use of electrolyte gel requires the use of thinner plates for proper distribution of the acid it means that a gel battery in marginal condition can literally shake the plates apart as the vehicle rides over rough roads.

Recombination Batteries
Recombination batteries recombine the gases formed during charging, keeping electrolyte concentrations optimum. They are completely sealed, never need topping up, and come with either liquid or gel-type electrolyte that is bound into the separators. There is no sloughing of lead and the plates in these batteries are tightly packed. The result is a powerful, compact battery with quicker charging time and a longer lifespan. The down side is often a higher price tag.

How Batteries are Rated
To help you determine what battery your car needs, batteries are rated by ampere hours (Ah), cold cranking amperes (CCA) and reserve capacity. These ratings tell you how much power a battery can produce under marginal conditions.

Ampere hours rate how much current can be drawn from a battery over a 20-hour period without voltage dropping below 1.75 volts per cell. A healthy battery should keep the parking lights lit for 20 hours. For powering accessories without the engine running, this is an important measurement.

Cold cranking amperes rate a battery's ability to start an engine under marginal conditions. CCA measures how much current can be delivered in amperes for 30 seconds at minus-18 degrees Centigrade (zero degrees Fahrenheit) with a final voltage of 7.2 volts per cell or higher. If you live in a cold-weather climate, you want this number as high as possible.

Reserve capacity, measured in minutes, tells how long a battery can keep the engine going if the alternator fails. During this test, 25 amperes are drawn from the battery for as long as voltage does not drop below 10.5 volts. Any battery you purchase should have a reserve capacity of at least 120 minutes, so you can always make it home.

Finally, always buy a battery rated for the vehicle and all the accessories it uses. Generally, this means a high Ah, high CCA, and high reserve capacity. Buy a quality, name-brand battery. Those sold in no-name battery discount stores are often poorly assembled and use inferior materials in the plates and separators.










good luck
jamie

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