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.
Absorbed glass mat (AGM) batteries...
Absorbed glass mat (AGM) batteries self-discharge slowly and therefore last longer in cars that see only intermittent use.
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.
Flooded batteries have been...
Flooded batteries have been the most common automotive batteries for almost 100 years. Their big advantage is price, as they usually cost about half of an AGM battery. Their self-discharge rate is high, and that can cause premature failure in cars that are not driven at least weekly.
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.