A lot has changed since Cadillac introduced the first practical electric starting system almost 100 years ago. That system employed a starter, generator, lights, and a lead-acid battery. Today, lead-acid chemistry is still at the heart of the automotive battery. That doesn't mean all automotive batteries are the same; there are important options to consider when it's time for replacement. First however, we'll look at how to preserve and test your batteries.
Maintenance and Storage
All types of batteries self-discharge. Over time, batteries will lose their charge even if nothing is connected to them. Rechargeable AA nickel-metal hydride (NiMH) batteries loose it quickly, while others, like disposable lithium batteries, can hold most of a charge for years. The self-discharge rate of lead-acid car batteries falls in between, but it has one crucial difference. Lead-acid batteries left at a diminished state of charge will suffer irreparable harm and will be significantly reduced in their capacity and useful life. When a car battery is even partially discharged, a hard crystalline insulating compound begins to form on the internal working surfaces in a process called sulfation. Sulfation is degenerative and largely irreversible. One modern type of lead-acid battery, the absorbed glass mat or AGM, is much less susceptible to self-discharge and is therefore worth considering for any application that sits for extended periods of time.
The number-one maintenance task, therefore, is to keep the battery fully charged. This has become more important today because modern cars are loaded with electronics that slowly drain the battery even when the car is not in use. As a rule of thumb, driving the car at least once a week prevents battery drainage from being a problem.
For cars that sit weeks or more at a time, battery life can be significantly extended if a special type of battery charger, a maintenance or float charger, is connected. This alone can make a seldom-used battery last seven to eight years instead dying in two years or less. A microprocessor-controlled smart charger will automatically decrease the current and voltage as the battery nears full charge. At full charge, it will either shut off or reduce voltage so as not to overcharge the battery, which is a real danger if a regular charger or trickle charger is left connected for too long. If the car will sit for several months, remove the battery and place it in a cool, dry location, but still place it on a maintenance charge.
Self-discharging is not the only way a battery runs down. Battery life is shortened if lights or accessories are used for long periods while the engine is not running. Automotive batteries are designed to produce a lot of power for the few seconds it takes to start an engine. That only drains the battery of about two percent of its capacity. The rest of the capacity is there to offer enough reserve power if the radio or lights drain the battery when the engine is off. Every time an automotive battery is drained significantly (like when interior lights are left on overnight), the battery's life is decreased. If this happens, place the battery on a charger as soon as possible.
The number two maintenance task only applies to batteries that have removable caps. Check the water (electrolyte) level every few months during cooler weather, but check more often when it is very hot. Only add water when the battery is fully charged, and then add only distilled water. The exception to this is if the water level drops below the plates, then add water just to the top of the plates and charge the battery. The water level rises as a battery charges.
The number three maintenance task is checking the battery terminals and battery cable ends for corrosion, and making sure they are snug.
Batteries last about four years on average in North America. However, in the hot southern states, automotive batteries often fail in three years or less, even sooner in the hottest climates like Phoenix or Las Vegas. So how can batteries have seven-year warranties? Read the small print. All but the first year is usually prorated, and this amounts to little more than an inducement to buy the same brand when it fails. My advice: Look at the free-replacement warranty time. For example, Optima's automotive batteries have a three-year free-replacement warranty.
Batteries differ by application, chemistry, and capacity. The application is a fairly easy choice. Automotive batteries (often labeled SLI for Starting, Lights, Ignition) are designed to deliver a lot of power for starting but get little use when the motor is not running. Optima goes a step further in identifying applications by color-coding its batteries. Automotive starting batteries are red topped. However, if your car has a 1,000-watt aftermarket stereo and you play it for hours at the beach every weekend, a dual-purpose battery, like Optima's yellow top, is a better choice. This second application type is designed to handle a deeper amount of discharge but still provide enough amps for starting. The third application type, the deep-cycle battery, is designed to last longer when drained repeatedly. Deep-cycle batteries, such Optima's Blue top series, are best suited for boat trolling motors, golf carts, and RV power.
Automotive battery chemistry boils down to two main options: flooded and AGM. Flooded batteries are available in two varieties, but both have acid sloshing inside. One version has removable battery caps to check the electrolyte level and add water when needed. These are said to have the highest rate of self-discharge. The other version of the flooded battery does not have removable caps and often is labeled maintenance-free. However, that doesn't mean it is sealed, as you'll discover if you tip it over. Flooded batteries do have the advantage of lower initial cost, about half that of an AGM battery.
Corvette owners should know the disadvantages of flooded batteries. Flooded batteries will mist, expelling droplets of acid under certain conditions. This can lead to corrosion of the battery terminals, battery cable ends, and surrounding parts. Flooded batteries can also expel hydrogen, which is explosive in concentration. When mounted in the passenger compartment (in C3s, for example), use care when charging them. Flooded batteries also self-discharge faster than AGM batteries. Therefore in seldom-used vehicles, flooded batteries need more maintenance.
The AGM battery uses an absorbed glass mat to hold the electrolyte between the lead plates. An AGM battery doesn't slosh like a flooded battery because the mat is designed to absorb all the electrolyte. In fact, it can be mounted on its side, and it won't leak acid even if its case is broken. This also means there's no need to add water. Positioning the mat solidly between the plates makes the battery much more resilient to vibration, too.
If unused, AGM batteries can last eight to twelve months (when disconnected) and still start the car. They have more starting power than similar flooded batteries. AGM batteries maintain higher voltage during cranking, which is critical to some aftermarket electronic ignition systems. They are more likely to recover after being discharged. There is no acid misting-so no corrosion-and there is no gassing. AGMs can have a considerably longer free-replacement warranty. And AGMs can last much longer. Optima states that its batteries typically last more than twice as long as flooded batteries.
Once you've settled on a battery type, the next choice is capacity. Choose a battery with cold cranking amps (CCA) equal to or more than what is specified for your car. However, if you have increased compression, more cubes, or need to start in very cold temps, consider a battery with a higher CCA rating.
The third choice is the brand, and there are many. Most are private-labeled; there are only a few major U.S. automotive battery manufacturers, with Johnson Controls said to be the largest. When shopping, find out how old that "new" battery really is. Look at the manufacture date code stamped on the battery case. Avoid a flooded battery that has been sitting on a shelf self-discharging for over four months. This is not as much of an issue with AGM batteries because of their significantly lower self-discharge rate.
With a little knowledge and maintenance, your automotive battery can provide reliable service for many years. And then every time you turn the key, you'll be happy to hear that rewarding sound of a big V-8 coming to life.
Battery replacement is easy, but automotive batteries are heavy, can have acid in or around them, and have to be brought back to the store for the recycle deposit. Before installing a new battery, charge it if recommended by the manufacturer or if it is not fully charged. For batteries with removable caps, recheck the electrolyte level after it has cooled and fill to the mark with distilled water when needed.
Battery Testing and Tools