Ask a person when their battery ran out last and see what look appears on their face, a mixture of lingering annoyance and dark humour, since the incident is almost always occasioned by poor timing to the point of cinematic. First date, job interview, middle of January, furthest corner of a multi storey car park. Car batteries possess a near supernatural ability to find the moment of failure, but the reality is much less mystical and much more chemical the battery did not choose that dreadful Thursday morning, it just finished an entropy process that had been operating in the background all throughout the months as day in day out the battery received no incentive whatsoever to be conscious of it.

Lead-acid batteries, such as those used in the vast majority of conventional vehicles, wear out by the chemical reaction that is not based on the calendar at all but rather on cycles and temperature exposure. Every single charge-discharge cycle that is done throughout the entire service life of the battery is a contribution to sulfation, the cumulative formation of lead sulfate crystals on the internal surfaces of the plates which permanently diminishes the effective electrochemical active area and cannot be regained in the course of regular charging once it forms in large amounts. The dimension that most drivers are surprised by is the temperature dimension since the timing of the battery failures is reversed due to the fact that cold weather is seen to cause the batteries to die when summer is the one that inflicts greater structural damage.

The usage pattern that silently kills more batteries than most individuals have appreciated is short trip driving and its killing is done by an arithmetic that is easy to understand once it is explained. Each cold start causes a large load of current through the battery to start the starter motor and the ignition system and the alternator requires a few kilometres of sustained highway or arterial driving to replace what it took to make the start. Any car which travels two or three kilometres, then stops, never goes through that restoration process, and the imbalance mounts up day and week after day until the available reserves are worn down to a level when a frosty morning, or an overstretched accessory load, throws the balance into a no-start condition.

The electronics installed in modern vehicles have increased the performance requirements of the battery over the performance requirements that cars needed even ten years ago, and this difference is what has contributed a significant portion of the premature replacement that is falsely attributed to a bad lot or an inexpensive component.