Like people, car batteries age over time and have a finite lifespan. Even in ideal operating conditions, batteries gradually deteriorate until they can no longer provide enough power to start an engine. When the battery is too weak to turn over the engine, the vehicle will need a proper boost or jump to start. To avoid this situation, a battery should be replaced before its capacity drops to the critical level. A battery lasts longer if the vehicle is driven daily and the battery is kept at a full charge.
After three years, it's normally time to install a replacement battery. After four or five years, most car batteries will be almost completely unreliable. Old car batteries can present a number of safety and reliability issues.