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Batteries - How Do You Know You'll Have the Juice When You Need It? by Brendon Turner
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.
Conventional Batteries
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 the negative plates in the battery are connected, as are all the positive plates. Each plate has a grid construction, and to this grid, the 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 the battery discharges (supplies electricity), the acid in the electrolyte reacts with the active material in the battery plates, forming lead sulfate and weakening the electrolyte solution. Conversely, as the battery is charged, the acid is returned to the solution, thereby strengthening it, and the used portion of the lead sulfate is converted back into active material in the plates. During this process, hydrogen and oxygen molecules are off-gassed out of the 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 the plates. Over time, this builds up in the bottom of the case, reducing the overall capacity of the battery fluid. When enough material builds up, the plates will short out, and you're stuck with a dead battery.
Maintenance-Free Batteries
Closed (maintenance-free) batteries are essentially the same as conventional batteries, except that they contain extra electrolytes in the partially sealed case. However, over time, this excess fluid is used up as fluid slowly off-gases hydrogen and oxygen molecules through the vents. Because these batteries cannot usually be topped off, once the plates begin to be exposed, the 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 the engine), a maintenance-free battery may not outlast a conventional one.
Another type of maintenance-free battery is the 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 the use of thinner plates so that adequate dispersion of the acid through the 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 the plates, premature reduction in electrolytes, and eventual battery failure. This means that during the harsh vibrations associated with trail riding, a marginal gel battery can fail completely as the plates literally fall apart.
Recombination Batteries
The recombination battery is overall the best battery for off-road and heavy-duty use. They're called recombination because they recombine the gas formed during charging, channeling it into the separators so it doesn't vent out of the battery and reclaiming the 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 the acid is bound into the separators and pure lead can be used in the plates. Because of the purity of the materials used, there is no sloughing and the 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 the 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 the case is damaged, and won't leak in a rollover. In short, for off-road use, they are just about the 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 the most common.
Ampere hours are determined by the SAE 20 test. This test is designed to show the amount of current that can be drawn from a battery for 20 hours without the voltage dropping below 1.75 volts per cell. In real-world terms, this means that a healthy battery should be capable of keeping the parking lights lit for 20 hours. For starting your truck, Ah doesn't mean much. However, for powering accessories without the engine running, this can be an important measurement.
Cold-cranking amperes or CCA is the unit of measurement that generally determines a battery's ability to start your engine. CCA is a measurement of the worst conditions under which a battery can be expected to deliver current, and it tests how much current in amperes a battery can deliver under extreme cold. According to the American SAE standard, CCA is determined by measuring how much current can be delivered in amperes for 30 seconds at -18 degrees C with a final voltage of 7.2 volts per cell or higher.
Reserve capacity is an important measurement for the total capacity of the battery and shows how long a battery can keep the engine running if the alternator/generator fails. Reserve capacity of a battery is measured in minutes at room temperature (approximately 70 degrees F). During this test, 25 amperes is drawn from the battery for as long as the voltage does not drop below 10.5 volts. For off-road use, it's a good idea to make sure any battery you purchase has a reserve capacity of at least 120 minutes.
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