Originally Posted by Rusty

The avg life of a car battery is 3 to 5 yrs. You get anything over that, the stars are in alignment for that battery. The life span of a battery is dependent on a few things. Age. The number of times it has been deep cycled. That is draining the battery to almost zero volts, and bringing it back up. If the battery has run low on water, if the plates has been exposed.

The plates in a battery get a build-up of sulfate on them over time. If the sulfate breaks off the plates in a big enough piece. It will short out 2 plates next to each other. Causing a dead cell. Each cell is good for 2.2 volts. what causes the sulfate to break off. Age, it just fakes off. Running low on water and exposing the top of the plates. Air hits it and causes a reaction. Vibrations in the car.