How to Buy a Car Battery

Batteries may look alike, but they don't perform alike

Most car batteries look the same on the outside: Save for a few variations in color, they all appear to be the same bland boxes. Even though more than a dozen brands are on the market, most are built by one of three manufacturers.

But don't assume that this means they all work the same way. Reliability, performance and life expectancy can vary greatly and spending more money doesn't always get you a better battery. Ratings differ even between brands made by the same manufacturer. For example, Johnson Controls makes both DieHard and Interstate batteries: The former has consistently high ratings, and the latter fluctuates, according to one consumer organization.

Standard car batteries are made of lead-acid components. They are also called wet cell or SLI (starting, lighting, igniting) batteries. Their main purpose is to start your car and power electronics. Two heavy-duty options are also available. Gel batteries mix a silica gel with the acid to prevent leaking and spilling. AGM (Absorbed Glass Mat) batteries place an electrolyte-laden mat made of boron-silicate glass between the plates; it's a setup often used in deep-cycle batteries. Overall, most batteries are maintenance free, though a few still include removable caps so you can check the battery's water level.

Where you purchase your battery can be important when it comes to warranty coverage. Some locations keep track of your purchase date in their computer, but even if your auto center does this, you should still always hang on to your receipt.

Keep these considerations in mind when shopping for a vehicle battery:

• Battery life is usually between three and eight years. This means that in all likelihood, you'll replace the original-equipment battery during the life of your vehicle.  When you're shopping for a new battery, it's crucial that you pay attention to both the free-replacement and, if applicable, the pro-rated warranties.

• Get the right size. Standard battery sizes include 24/24F, 34/78, 35, 65 and 75. The right battery for your car will properly fit in the battery tray and provide the correct amount of power to crank your engine. The size also determines where the battery terminals are -- on the sides or on top -- so they line up correctly with your battery cables. Some sizes, such as 34/78, have terminals in both positions, allowing you to select the ones that work best for your car.

• Consider your area's extreme temperatures. Freezing temperatures place additional strain on a car battery: The battery must overcome thicker motor oil to turn over the engine while combating a power loss from the cold weather. Selecting a battery with high cold-cranking amps (CCA) is key. This measurement tells how much power the battery has at 0 degrees Fahrenheit. High temperatures bring on a burden of a different kind. A leading cause of battery failure comes from the loss of electrolytes, and heat speeds up this process. Just as there are northern versions of most batteries, you can also find southern variants with components that are designed to better withstand intense heat . They include thicker plates and more electrolytes, for example. Ultimately, that may not mean a lot in particularly harsh hot-weather regions. AAA Arizona says, for example, that the average lifespan of a battery in Arizona is 22 months. After that, regardless of what the warranty states, AAA says the battery is "on borrowed time" and should be tested.

• Batteries with handles are easier to carry and install. On average, a standard battery weighs between 40 and 50 pounds. Lifting this dead weight up and into your engine compartment can be cumbersome; a handle goes a long way in helping. It also keeps your hands off the battery, which in turn makes it easier to lower the battery onto the battery tray and keeps your hands clean if you're removing a leaking battery.

• Some cars are better suited to high-performance batteries. Additional electronics, such as enhanced audio/video/entertainment systems, require more from a battery than the average vehicle, as do some high-performance or heavier-duty vehicles. High-performance batteries often substitute the common lead-acid core with higher-quality components like absorbed glass mat or gel. Some brands also combine powerful starting capabilities with the stamina of a deep-cycle battery.

• You may have to pay a core charge. Most auto parts centers add a core charge or disposal fee to the battery price. If you're exchanging an existing battery at the time of purchase, this charge likely will be waived. And if you bring back your old battery after the fact, it'll probably be refunded then.