This will shorten their life and reduce their capacity. Inactivity can be extremely harmful to all lead acid batteries. Store the battery in as cool a place as possible. 32 F. Batteries will discharge when stored, the lower the temperature the lower the self discharge. When not in use, boost every two months.
Extreme temperatures can substantially affect battery performance and charging.
Cold reduces battery capacity and retards charging. Heat increases water usage and can result in overcharging.