Important things to avoid when storing batteries:
Freezing. Avoid locations where freezing temperature is expected. Keeping a battery at a high state of charge will also prevent freezing. Freezing results in irreparable damage to a battery's plates and container.
Heat. Avoid direct exposure to heat sources, such as radiators or space heaters. Temperatures above 80° F (26.6°C) accelerate the battery's self-discharge characteristics. For every additional 15 degrees of heat over 77 deg F (25°C) , lead acid battery life is cut in half. Batteries self-destruct with time, you can only slow that process.
Step by step storage:
Store the battery in a cool, dry location, protected from the elements.
During storage, monitor the specific gravity (flooded) or voltage. Batteries in storage should be given a boost charge when they show a 70% charge or less.
Completely charge the battery before re-activating.
For optimum performance, equalize the batteries before putting them back into service. Refer to the Equalizing section for this procedure.