Battery Size

• The vehicle's owner manual or in-store fit guide help explain the type of battery that will fit a car and whether it uses top- or side-mounted terminals. For example, a size 65 battery with a top terminal is used for trucks and large cars. A size 75 battery is normally used for mid-size and compact cars.
  
  

Service Life

• Service life is one of the most important considerations when choosing a battery. Since all batteries lose their ability to retain charge over time, look for a battery that is six-months-old or less from the date of manufacture. Look at the manufacturing date stamped on the battery case or label to get an idea of how long the battery should perform.
  
  

Brands

• Most car battery brands offer different warranties and prices vary significantly. A well-known car battery brand is the most cost-efficient in the long run due to the longer warranty and longer battery life. It is estimated that battery prices vary from $90 to $300 (as of January 2011). Cheap generic brand batteries are more likely to break down and are considered more unreliable. Battery size, cold cranking amps (CCA) and warranty are the biggest factors affecting cost. CCA measures the car's ability to start under freezing temperatures.
  
  

Special Features

• Some batteries have special features that may provide you with a better deal. Absorbed glass mat (AGM) battery manufacturers claim AGM batteries are the safest because they will not spill acid. Although AGM or dry cell car batteries are more expensive, they are expected to last three times longer than conventional wet cell batteries.