This fellow wrote a dissertation on automotive starting batteries and deep-cycle batteries:
Here are just a couple key excerpts from his very useful site at
http://jgdarden.com/batteryfaq/carfaq7.htm
"For car batteries, select the battery with CCA (Cold Cranking Amps) that will meet (or just exceed the vehicle manufacturer's recommendation), or is best suited for the coldest temperatures encountered in your climate. This is because more CCA requires greater plate surface area and in order to fit more surface area in the same space, this means thinner plates. Thinner plates will normally cause shorter overall service life. Do not substitute CA (Cranking Performance Amps), MCA (Marine Cranking Amps), or HCA (Hot Cranking Amps) for CCA. In hot climates, buying batteries with double or triple your vehicle's cranking amp requirements is usually a waste of money. Unless starting batteries are used in extremely cold climates, increased CCA is required to crank a sluggish engine and over come inefficiency of a cold battery. James W. Douglas' recommendation in his February 2000 article, Battery Selection--A Consumers Guide, in The Battery Man magazine, is:
"The sleek, aerodynamic designs have low cooling airflow through the engine compartment and that small in stature battery with high cold crank [amps] will have many very thin lead plates just to get the necessary surface area to make that big cold crank number. It will have a lower volume of electrolyte to provide the cooling necessary for long life and the greater capacity to run the [electrical] systems on the car. All of those thin plates will corrode away and fail long before expected putting the high performance battery's life below that of the lower CCA rated battery with the lower cost. Your best rule-of-thumb is, if it meets the OEM (Original Equipment Manufacturers) recommendation, buy it. Look for the highest reserve capacity [RC] battery that meet your CCA (Cold Cranking Amps) requirement for your climate."
7.8.4. More Reserve Capacity (RC) or Amp Hours (AH) is a good
thing.
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AND this excerpt:
"Freshness
Lead-acid batteries are perishable and sulfate in storage due to their natural self discharge, especially in temperatures above 80° F (26.7° C). Please see Section 16 for more information on sulfation.
"Determining the "freshness" of a battery is sometimes difficult. Unless it has been periodically recharged or is "dry charged" (shipped without electrolyte), NEVER buy a wet Standard (Sb/Sb) or Low Maintenance (Sb/Ca) battery that is MORE than three months old or a wet "Maintenance Free" (Ca/Ca) battery that is MORE than six months old. Dry charged batteries are shipped without electrolyte, but usually have "sell by" dates of one to three years. Depending on the temperature, AGM (Ca/Ca) and Gel Cell (Ca/Ca) batteries can be stored six to 18 months before the State-of-Charge drops below 80%. Please see Section 16. for more information on sulfation.
"Dealers will place their older batteries in storage racks so they will sell first and they do not have to maintain them. The fresher batteries generally can be found in the rear of the battery rack or in a storage room. For a wet battery, the date of formation is often stamped on the case or printed on a sticker. If at all possible, have a new battery measured with a digital DC voltmeter or tested. Recharge if necessary, before the battery leaves the store. This can save a lot of time and frustration if the new battery is discharged, sulfated or has a manufacturing defect."
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And this:
Pick the battery type that matches your charging system, application and driving habits.
"For starting an engine, using a car or starting battery is normally a better choice than a deep cycle battery because it is specifically designed for shallow (1%-5%) discharges. The battery type MUST match the vehicle's charging system or the new battery or charging system could be damaged. The easiest way to accomplish this is to replace your battery with the same or compatible type of battery that was originally installed by the vehicle's manufacturer. The exception to this is in hot climates, using a non-sealed wet "Maintenance Free" car battery (with filler caps) is highly encouraged because lost water can be easily replaced. For batteries with side terminals commonly found in General Motors vehicles, check the terminal bolt length and do not over-tighten because you might crack the battery case and cause a leak. Driving habits also is a consideration. Non-use over a week or especially in the winter, short trips of less than a mile, will not keep the battery fully recharged. This could cause a gradual accumulation of lead sulfate which can prematurely reduce the performance and capacity or a frozen battery.
"For a deep cycle application, using a deep cycle battery is a much better alternative than using a starting battery because the deep cycle battery will have a much longer service life when deeply (50% to 80%) discharged because the plates are thicker."
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Again, here's his helpful web site with lots, lots more information (about 50 pages worth):
http://jgdarden.com/batteryfaq/carfaq7.htm
