What size battery do you need? Batteries come in various sizes called "Groups." You can find the size on your battery or in your car owner's manual, or the store clerk can look up the size by your car's make and model.
Do you live in a hot or cold climate? Choose your car battery accordingly. Hot-weather batteries, often labeled "South" or "S," are designed to endure extreme heat. Cold-weather batteries sometimes labeled "North" or "N" have higher cold-cranking amps (CCA).
Do you need a high-performance battery? Probably not, experts say, if you drive an ordinary car. But if you have loaded your car with power-hungry goodies such as power amps, extra lights and more, you might want to spend extra for a high-performance battery like the Optima YellowTop D34/78 (Est. $210).
Do you drive off-road? Consider the Optima brand. Instead of fragile plates inside, Optima batteries have sturdy coils that stand up better to constant vibration.
Do you want it installed? Garages, most auto-parts chains and some other stores including Walmart will install your battery for free if you buy it there. Sears charges extra for installation (Est. $10), and Costco doesn't install batteries at all.