Generally, the average car battery life is between three and five years. Many variables, however, can make the difference between replacing your car battery at three years, and replacing it at five. With proper attention and usage, it is possible to get full value out of your battery, whether it is a replacement purchase or it came with your car.
The average car battery is built on the same technological platform as car batteries of 100 years ago. Car batteries are typically lead acid batteries. Electrical power is stored in a liquid chemical form and released on demand. You can use your car battery continuously, without recharging it, for two hours before it drains completely. The alternator acts as an electrical generator to recharge the battery, but only while your car is running.
If you keep your battery maintained properly and recharge it regularly, it should give you close to five years of service. When you store your vehicle for long periods of time, disconnect the battery at the terminal connections. This will stop parasitic drain from applications, like clocks or stereo displays that run while the ignition is off. Also, the battery will drain if left in very hot weather without starting the ignition at least once every 48 hours. Also, if your battery has fluid reservoirs, you must keep these filled. In extreme heat, this fluid can evaporate and will damage the internal components of the battery.
If your battery is drained to a zero charge, you can recharge it by connecting your battery to the terminals of a battery in a running vehicle; or by using a trickle charger, and slow-charging it overnight. While draining the battery to a zero charge will not "kill" it, it will reduce the potential battery life every time it is drained.
To make sure your battery lasts as long as possible, get into the habit of servicing it once every six months, or have a service person inspect it when you get your oil changed. Maintenance is the key to long battery life and getting the most value possible from your battery.
Car batteries contain dangerous chemicals that can damage clothing and burn skin and eyes. When working around auto batteries, remember to ensure your safety first. Work in well-ventilated areas, always wear eye shields or safety goggles, and be aware of what needs to be done in the case of a spill or accident.