If you don't use your car for a long time, my understanding is that the battery will go into a deep cycle discharge because the BCM and security systems use a small amount of power even when the ignition is off. This type of discharge is the worst type of discharge for a starter battery, especially in the winter. This is the reason boats or recreational vehicles that get occasional usage use deep cycle or marine batteries. These type of batteries can be revived from deep cycle discharge.
The standard starter battery cannot be fully revived from this type of discharge. This is why people connect trickle charger to top off for weekend cars or disconnect the battery for storage.
If you use the car frequently, you won't notice that the battery has degraded, but it progressively will become worse at holding a charge. After all, the starter battery purpose is essentially to start the car. Once started, the alternator largely does the job.
