What is the recommended shelf life of a battery, and can I install one that has been stored?

Six months is the recommended maximum storage period for a VRLA battery without recharging. Beyond that, self-discharge allows sulphation to begin, and the capacity loss may be permanent. If batteries must be held longer, put them on a maintenance charge on a schedule. Record the date code at receipt, a battery that spent a year in a store has already consumed part of its life before commissioning, and this is a common and avoidable cause of early failure.