On average, car batteries last for up to four years depending on location, owner's driving habits, type of vehicle and other conditions. Normal conditions for a battery involve having full charge cycles, lack of extreme temperatures, a reliable and consistent charging system and only a small amount of other accessories.
A technician can use a battery tester while the battery is in the vehicle to determine how the battery is operating. Other factors can determine battery life, such as the driver only taking short trips which would not allow the car's charging system to replace the huge amount of energy required to start the car. Corrosion or stains around the terminals of the battery mean there is an acid leak, which is typical of a dying battery. The presence of a rotten egg smell indicates an overheated battery which may soon need to be replaced.