Every day we expect both to perform flawlessly no matter what conditions and demands they face. But just as you can overtax your heart, you can exceed a battery's capabilities and neglect its most basic needs - and you may not recognize the damage until it is too late.
Fortunately, replacing a battery is relatively simple, though choosing a suitable replacement requires some forethought. Because of the availability of electronic aftermarket devices such as video and navigation systems, the original equipment battery may not be able to meet a vehicle's increased power demands. But unlike the heart, batteries have evolved, and you can upgrade to a stronger, longer-lasting unit that can easily keep pace with today's demands.
How a battery works
A traditional automotive battery (referred to as a flat-plate or flooded battery) is a storage device that converts chemical energy into electrical energy. Made up of six independent cells connected in series, each cell produces about 2 volts. Each cell contains a positive and a negative plate and is filled with a fluid made of sulfuric acid diluted with water. Typically, the positive plates contain lead dioxide, and the negative plates are composed of plain lead.
A battery has two cycles: discharging and charging. In the discharge cycle, a chemical reaction takes place in which the lead of the negative plates combines with the sulfur and oxygen molecules of the sulfuric acid to produce lead sulfate. The electrolyte becomes weaker, the positive and negative plates become more like one another, and the battery loses power. In the charge cycle, however, the reverse is true. Electric current generated by the car's alternator passes through the plates, forcing the sulfur and oxygen molecules out of the lead sulfate and back into the electrolyte bath, increasing the overall voltage, or charge.
Battery power rating is measured by two standards. The first standard, cold cranking amps, indicates the amount of current a battery delivers for 30 seconds at 0 degrees Fahrenheit while maintaining a minimum voltage of 7.2 volts - the higher the number, the stronger the battery and the more starting power it possesses.
The second standard, the reserve capacity rating, is an estimate of the number of minutes it takes a fully charged battery to dip below 10.2 volts at a continuous discharge rate of 25 amps. For example, a rating of 120 means the battery will run for two hours (120 minutes) before ceasing to function.
Changes in battery design
Though flooded batteries have served well over the years, changes in automotive design and aftermarket power requirements demand more performance from batteries than ever before. To provide more consistent power for those aftermarket applications, Sears has been working on a new manufacturing process for its Diehard line of batteries.
In the past, each plate within a battery was individually cast, and casting variations could result in shortened battery life. The new process uses a continuous casting system to create lead-alloy slabs from which the battery plates are individually punched out. The resulting consistent plate thickness allows the battery to hold a higher charge and to release that charge in a cleaner, more consistent flow for a longer period of time. The plates last longer, and the battery as a whole is more durable.
Another new technology to enter the automotive market is absorbent glass mat (AGM) design. With this type of battery, absorbent glass is sandwiched between the lead plates where it functions like a sponge, holding the acid in place. AGM batteries are expensive - they can cost twice as much as conventional flooded batteries - but they're spill-proof and more vibration resistant than their traditional counterparts. Optima, a longtime manufacturer of AGM batteries, has taken the concept a step further with its SpiralCell technology. With this type of battery, the absorbent glass mat is spiral-wound with the lead grids and placed in six individual cylinders within the battery case. Each cylinder is compressed, locked into place and sealed. The result, according to Optima, is a battery that emits no explosive hydrogen gas, is completely spill-proof, is more than 15 times more resistant to vibration and can have a lifespan two to three times that of a traditional flooded battery.
Spill-proof batteries are important because of changes in automotive design. For example, General Motors includes on many of its vehicles the On-Star system, which can summon help in the event of a crash. Like all systems on an automobile, On-Star relies on battery power to operate. And in many major accidents where the front of the vehicle is damaged, the battery can be damaged or disabled, rendering the On-Star system useless.
To better protect the battery, automobile engineers are beginning to relocate it from the engine to the passenger compartment. And in order to protect the vehicle's occupants, it's vital that the battery not emit hydrogen gas or spill any acid in the event of a rollover.
Battery maintenance
Just because there are great new advancements in batteries doesn't mean you should relegate your current unit to an early death. By following these basic testing and maintenance steps, you'll get the most life out of your battery, and you'll know when it's on its last volt.
Before doing any maintenance on a battery, remove the cables. Check the owner's manual first to make sure that vital information such as remote key-lock codes won't be lost. Depending on the style of battery and type of cables the vehicle is equipped with, use either a battery-clamp removal tool or a proper-fitting wrench to remove the clamps from the posts. Work gently to avoid breaking the terminal posts.
Though you can use a simple voltmeter to check the battery (which should read about 12.6 volts with the engine and all electrical draws turned off), the best way is with a battery load tester. A load tester does more than indicate the amount of charge a battery has; it also indicates the battery's ability to hold and deliver that charge and measures the vehicle's ability to create enough electricity to keep the battery in tip-top shape. Different brands of load testers have slightly different directions for usage - to avoid injury, always follow the tester's instructions.
Another way to test a battery's condition is with a hydrometer, an instrument that measures the specific gravity of the battery acid. To use a hydrometer, first draw electrolyte into its tube. (Older types of batteries had inspection caps that provided access to the fluid within a battery, and many so-called "maintenance-free" batteries still have removable covers hidden beneath stickers.) Hold the hydrometer vertically at eye level so that the float is free to move. Check each individual battery cell separately - the higher the specific gravity, the more charge in the battery (see photo, above right). In general, a fully charged battery will have a specific gravity of 1.275. A weak battery will have a specific gravity of 1.250 to 1.225. A discharged battery will have a specific gravity of 1.200 or less.
To get the most accurate reading, adjust the hydrometer's measurements according to the electrolyte's temperature. If it's above 80 F, add .004 to the hydrometer reading for each 10 degrees above 80 F. If the electrolyte temperature is below 80 F, subtract the same amount from the hydrometer reading for each 10 degrees below 80 F.
As an additional preventive measure, after you've tested the battery, use a wire-brush-style post cleaner (see bottom right photo) to remove any residue that creates electrical resistance. Use a baking soda paste and a toothbrush to dissolve any trace amounts of battery acid; then replace the cables and coat the terminals with white lithium grease or a special battery-terminal protectant.
If your tests indicate that the battery is weak (or if you're just itching for a new battery), use what you've learned here to choose the type that best fits your needs. Through periodic inspection and maintenance, you'll be sure to get the most life from your new investment.