Modern vehicles make a lot of demands upon their batteries. We expect our batteries to be reliable, have a large reserve capacity and a long life span, and be maintenance-free. In short, once a battery has been installed, we no longer want to think about it. Here's some tips on how to choose a battery that will serve you well.
For automotive applications, there are basically three types of batteries: conventional, maintenance-free, and recombination.
A 12-volt automotive battery contains six cells. In each cell is a series of alternating positive and negative plates, between which are isolator or separator plates to keep them apart. All negative plates in battery are connected, as are all positive plates. Each plate has a grid construction, and to this grid, plate's active material - sponge lead - is bonded. The plates in each. cell are covered with a solution of distilled water and sulfuric acid (electrolyte). As battery discharges (supplies electricity), acid in electrolyte reacts with active material in battery plates, forming lead sulfate and weakening electrolyte solution. Conversely, as battery is charged, acid is returned to solution, thereby strengthening it, and used portion of lead sulfate is converted back into active material in plates. During this process, hydrogen and oxygen molecules are off-gassed out of electrolyte, which is why a conventional battery often needs topping up with distilled water. The charge and discharge cycle also means that some lead sloughs off plates. Over time, this builds up in bottom of case, reducing overall capacity of battery fluid. When enough material builds up, plates will short out, and you're stuck with a dead battery.
Closed (maintenance-free) batteries are essentially same as conventional batteries, except that they contain extra electrolytes in partially sealed case. However, over time, this excess fluid is used up as fluid slowly off-gases hydrogen and oxygen molecules through vents. Because these batteries cannot usually be topped off, once plates begin to be exposed, battery's life span is over. Usually, this takes a long period of time, which is why these batteries often last longer than conventional batteries. However, in situations where frequent, rapid charge/discharge occurs (such as when running a winch or powerful spotlight without running engine), a maintenance-free battery may not outlast a conventional one.
Another type of maintenance-free battery is gel-type battery While these batteries cannot leak or spill fluid and can be installed at odd angles, they do have a weakness. Using electrolyte gel necessitates use of thinner plates so that adequate dispersion of acid through active material occurs. Since gel batteries are also sealed, they cannot be topped off and care must be taken when charging so they don't overcharge and gas-off, which will result in excessive sloughing of plates, premature reduction in electrolytes, and eventual battery failure. This means that during harsh vibrations associated with trail riding, a marginal gel battery can fail completely as plates literally fall apart.
The recombination battery is overall best battery for off-road and heavy-duty use. They're called recombination because they recombine gas formed during charging, channeling it into separators so it doesn't vent out of battery and reclaiming water to keep electrolyte concentration at optimum. They are completely sealed (except for a reseating pressure-relief vent) and require no topping off of fluids. Recombination batteries can use either liquid or gel-type electrolytes and are different from other batteries because acid is bound into separators and pure lead can be used in plates. Because of purity of materials used, there is no sloughing and plates in these batteries can be very tightly packed. The result is a powerful, compact battery with quicker charging time, lower internal resistance than conventional or maintenance-free batteries, and a longer life span. In fact, for a conventional battery to deliver same amount of starting power as a recombination battery, it would have to be two or three times larger. Because they contain no liquid as such, recombination batteries can be mounted in any position, will work when case is damaged, and won't leak in a rollover. In short, for off-road use, they are just about perfect battery.
How Batteries Are Rated
Battery ratings are a determination of how much power a battery can produce under marginal conditions. There are a number of ways to determine a battery's output, but ratings by ampere hour (Ah), cold-cranking amperes (CCA), and reserve capacity are most common.
Ampere hours are determined by SAE 20 test. This test is designed to show amount of current that can be drawn from a battery for 20 hours without voltage dropping below 1.75 volts per cell. In real-world terms, this means that a healthy battery should be capable of keeping parking lights lit for 20 hours. For starting your truck, Ah doesn't mean much. However, for powering accessories without engine running, this can be an important measurement.