L/A batteries self-discharge at a rate determined by temperature and battery condition. When kept cool, below 50 degrees, the rate is about 5 or 6% a month. 90 degrees and above, the rate climbs to 15 or 20 % a month. So unless the stored battery is maintained by charging (choose your own method) it will slowly die. Once completely discharged, it quickly becomes scrap lead.
Even if kept charged, L/A automotive batteries have a 5 or 6 year shelf life. They simply degrade over time…