If you're like the majority of the motoring public about the only time you think about the battery in your truck is when you hit the starter and instead of a roar from under the hood there's a faint click. And, if your luck is like ours, that situation only occurs at the worst possible time and at the most inconvenient location.

Battery Basics
At one time choosing battery for a classic truck was simple enough, you bought another one just like the one that was there to begin with. But today there are more types and styles of batteries than ever and you should know what's best suited to your application before you buy.

All automotive batteries have one thing in common, they use a combination of lead and acid to produce a little over two volts per cell (as a result 6-volt batteries have three cells, 12-volts have six). The cells are made up of lead plates and an electrolyte solution that together causes a chemical reaction that releases electrons that flow through conductors to produce electricity. As the battery discharges, the electrolyte reacts with the plates, changing the composition of their surface. When the battery is recharged, the chemical reaction is reversed restoring the plates to their original condition and the process is repeated.

Although they produce electricity in a similar manner, there are three different configurations of lead acid batteries: wet cell, gel cell, and absorbed glass mat (AGM).

Wet Cell: Also called flooded batteries these use liquid electrolyte and come in two styles: serviceable and maintenance free. Both are filled with liquid electrolyte but as the names implies, water can be added to the serviceable style while the maintenance free is sealed.

Gel Cell: By using an additive, the electrolyte in these batteries stiffens and becomes a gel. In most cases these batteries are very sensitive to overcharging and premature failure may result.

AGM: These are unique in that the electrolyte is suspended in an absorbent fiberglass material, eliminating the need to flood the battery with liquid. This design makes AGM batteries spill-proof and vibration-resistant with the added advantage that they can be mounted in almost any position (however, upside down is not usually recommended).

Battery Applications
All batteries, regardless of their construction, will fall into one of two categories-starting, or SLI (which stands for Starting, Lights, Ignition), and deep-cycle.

SLI batteries generally have a high plate count and are designed to deliver a large amount of energy for a short period of time. Deep-cycle batteries are designed to deliver power continuously for a long period of time and are designed to discharge "deeper" than an SLI battery. Now to confuse the issue-a deep-cycle battery will very often function perfectly well in a starting capacity, however the reverse isn't true, using an SLI battery in a deep-cycle application will just about always shorten its life dramatically.

Battery Ratings Batteries are rated by their performance in a variety of categories:

CCA, or cold cranking amps, is a measurement of the number of amps a battery can deliver at 0 degrees F for 30 seconds and not drop below 7.2 volts. A high CCA battery rating is especially important for starting battery applications in cold climates.

CA is cranking amps measured at 32 degrees F. This rating is also called marine cranking amps (MCA).

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 80 degrees F will discharge 25 amps until the battery drops below 10.5 volts.

An amp hour (AH) is a rating usually found on deep-cycle batteries. If a battery is rated at 100 amp hours it should deliver 5 amps for 20 hours, 20 amps for 5 hours and so on.