Car batteries are much better today than they were even a few years ago. I've had batteries last as long as 9 years in a car, which is amazing. Only a few years back, the "60 month" DieHard car battery from Sears was considered the top of the line. Technology has improved over time.But car batteries can fail at any time, even when brand new. And although they can last as long as 9 years, typically most fail in the 5-7 year range, if not before. And cheaper batteries might not last even that long.The failure mode of car batteries appears sudden, which is something that confuses people. Most folks' experience with batteries is based on flashlight or other consumer product batteries. A flashlight battery fails slowly over time, getting dimmer and dimmer, until one day, it is a mere flicker and then goes out. Consumers think that this gradual failure mode applies to car batteries as well, which is why they dismiss the battery as the problem when the car "suddenly" fails to start. bmw tail lights
